The plug-in electric flu side hall effect technology provides a safe and reliable power electronic detection and protection
The plug-in electric flu side hall effect technology provides a safe and reliable power electronic detection and protection
The author Paul Emerald
Abstract
New power semiconductor (IGBT, MCT, etc.) shows the power output limit of progress, as an extension of the system development and the expansion of power semiconductors, sensing the current level of escalating these become increasingly clear precedent (parallel) requirements.Hall effect IC provides "plug-in" electric measurement technology, the flu can carry on the security to the high current level, isolation, detection, and won't dissipation of power (and synthetic heat), and this is the disadvantages of the resistance type electric flu test method.In addition, the hall effect electric conductor for flu test to provide electrical insulation;Therefore, for circuit system, operators, etc. To provide a safe environment.
In view of the hall effect IC electrical flu test application continues to surge, and even become more diversified.In other designers to protect the system, the hall effect IC application development and growth, and create a more reliable "flawless" equipment, at the same time solve any security problems.Cost-effective power of the hall effect sensor IC flu test main applications include:
- Current is not balanced
- Current monitoring
- The operator/user safety and security
- Over-current detection/protection system
- System diagnosis and fault detection
- Test and measurement
Background and introduction
People discovered the hall effect in 1879;However, in the late 1960 s before the emergence of semiconductor integrated, Edwin hall of the people not found any meaningful application.Since then, with the further development of technology, particularly in the 1990 s), the function is more complete, more special hall sensor IC integration and series.The advance of magnetic sensor electronics, lead to low cost, reliable "contactless" hall effect circuit system demand is also increasing, and used to test mobile sensor /, direction, position, and can be used to measure/monitor current.
Hall effect sensor IC (especially of linear type) is used in the "open loop" influenza a great device to test design.However, in the scope of work can be realized, the accuracy and precision, frequency response, etc, are limited.Because many expected users don't know and/or not aware of the use of hall effect IC electric measurement technology, the advantages or disadvantages of flu this article to use silicon hall effect device for "plug-in" electric flu basic measurement technology is synthetically discussed.
If you don't use grooved ring coil concentrate (focus) and induction magnetic field, hall effect electric measuring flu could not form enough magnetic field most application requirements.low电流至适度电流（<≈ 15 安培) 需要有槽环形线圈（铁芯）缠绕足够的圈数，才能感应可用的磁通强度并形成合适的信号电压。较高电流（>15 至 20 安培）感应的磁场强度使载流导体能够直接穿过环形线圈中心（这些较高的电流不需要缠绕线圈）。
For wide (or continuous) current scope of design, need to use the linear hall effect sensor IC.But may be digital, hall effect device over current protection and/or fault detection design.This article about sensor hall effect device used in the alternating current and direct current flu paper covers electricity measurement technology of instance and the basic elements of details, and the device parameters, temperature stability and other problems related to electrical flu hall effect test.
Competing technologies
Although there are many electric flu test method, but common in the application of low cost, large quantities of only three.Other is expensive laboratory system, the emerging technology (such as magnetic resistance technology) or rarely used technology.Commonly used techniques include: (1) resistance, hall effect (2) and (3) current transformer.
Resistance sensor is widely used, low cost, easy to understand.However, the shortcoming of this technique is the insertion loss (heat and dissipation power) and the lack of isolation.Moreover, many power resistor series inductance constraints, the frequency range of the low cost parts;Therefore, according to the categories in table 1, the resistor sensor for dc or ac applications.Used for high frequency low inductance, high power resistance is more expensive, but the work frequency can be more than 500 kHz.And resistance type electric technology (usually) flu test signal amplification (need to use the comparator or operational amplifier).
| Table 1: common flu cheap electricity measurement technology | |||||||
|---|---|---|---|---|---|---|---|
| The sensor is widely used | Power consumption |
Circuit isolation | Frequency range | size | accuracy | Relative cost | |
| Insertion loss | External power supply | ||||||
| Detecting resistor + optical amplifier | High voltage | low | low | Dc to 10 MHz | In the | Plus or minus 3 to 5% | low |
| Standard open loop hall effect | low | low | high | Dc to 50 kHz | small | + / - 5 to 10% | In the |
| Hall effect of closed loop | low | In the | High voltage | Dc to 1 MHz | In the great | "Plus or minus 1% | high |
| Allegro open-loop hall effect current sensor IC | low | low | high | Dc to 120 kHz | small | Plus or minus 2 to 3% | In the |
| The current transformer | (AC) | There is no | high | 60 Hz to 1 MHz | In the great | Plus or minus 3 to 5% | high |
| * current transformer is usually run in a limited frequency range, but can be designed for low to high frequency. | |||||||
Hall effect sensor IC (open loop and closed loop) represents another level of the common solution.Insertion loss (and related heating, etc.)notObstacles.However, compared with resistive sensor method, hall effect IC technology in the frequency range, cost, which has potential disadvantages dc offset and the external power supply.
Current transformer is the end of the last generation of low cost technology, but can only be used for alternating current transformer (as the term implied meaning).Most of the current transformer design on a narrow frequency range, low cost is more expensive than resistive or hall effect, andCan'tUsed for direct current.However, current transformer to avoid the insertion loss, provide electrical insulation,Does not require an external power supply,In no offset voltage zero current.
Because this article discusses the hall effect IC, understand the ratio of linear measurement principle of hall effect device split ring electric flu is necessary
The linear hall effect sensor IC
Are shown in this term, the linear hall effect sensor IC produce an additional magnetic field is proportional to the output signal.Usually, in any electrical flu test applications, the magnetic field by a "grooved ring coil focus, in order to form enough magnetic field intensity, and the magnetic field generated by the current in the conductor induction."Classic" ratio of linear measurement transfer curve is shown in figure 1.Please note that the scope of each point, the output reached saturation point.
Figure 1.The linear hall effect sensor IC transfer curve
The latest linear hall effect IC provides ratio measurement output voltage.Voltage is static (i.e., zero) plus a steady 50% of the nominal voltage.The equivalent static output voltage signalThere is noPlus a magnetic field, for electricity, flu is equivalentzeroElectric current.The Antarctic magnetic field caused by positive voltage conversion (toward VCC), the arctic cause toward the earth magnetic field (0 V) conversion.Output saturation voltage (typical) of 0.3 V (high/pull) and 0.2 V (low/irrigation), and measuring in the plus or minus 1 mA.[Editor's note, the output voltage in the millivolt range.]
Each linear hall effect IC integrates a sensitive hall element (also known as the "board"), a low noise amplifier (bipolar), and irrigation/pull output stage.Magnetic hall effect devices, amplifier, the output and associated signal processing circuit of single chip IC will any system problems on low signal and noise to a minimum extent.
Existing very stable linear hall effect device using dynamic orthogonal offset elimination circuit and electronic switch to change the current path of hall element.With high repetition rate will current path switch from 0 ° to 90 °, for a long time influence the stability of the linear sensor IC run and dc offset (natural) provides a new solution.
Using sampling keeping circuit and low pass filter to the innovation of the internal dynamics of the linear hall effect device signal is an appropriate reduction.
Linear hall effect IC can detect small flux intensity changes, in terms of electric measuring flu, (usually) is more useful than digital hall effect IC.Linear hall effect device often capacitively coupled to the operational amplifier, or dc connection to the comparator, in order to achieve system design.In addition, the micro controller (including C) and the microprocessor (including P) to detect the weak signal of linear hall effect IC change, and very suitable for () with the appropriate software sensor/measuring ac or dc current.
Induced magnetic field
As mentioned earlier, hall effect electric measuring flu usually need to use the grooved ring coil (made of ferrous material).Circular coil induced magnetic field in IC assembly to the position of the hall effect element concentration and focus.Figure 2 is the use of slotted toroid "plug-in" electric flu test of typical examples.Conductor of electric current flows through the winding on the circular coil turns, induction flux field is concentrated in the annular coil gap (or slots) in sensor IC.Generally, the gap and the thickness of hall integrated circuit encapsulation (about 0.060 "or 1.52 mm) is very match, to provide the optimal magnetic coupling.Current (at the "close" magnetic coupling) induction flux intensity according to the following formula:
B (gaussian) material N (number of turns) x 6.9 gauss/amp
[Editor's note: from the previous 6 gauss/amp gaussian/update 6.9 amps.]
Figure 2.Use the band gap of toroidal coil electric measuring flu
Widen the slot (gap) will reduce the magnetic flux coupling and increase the current limit, which is based on the sensitivity of hall sensor IC for prediction (behind will introduce more details).However, the induced magnetic field decoupling to extend the maximum current limit, may affect the linear, usable range, etc.This "loose coupling" is in evaluation stage, has not been completed;As a result,There is noRecord under the condition of big gap, in view of the new formula of magnetic flux and current conductor.
"Calibration" ratio measured linear hall effect device
Two kinds of the latest [Editor's note: articles published in 1997] linear hall sensor (with dynamic dc offset elimination) for the linear hall effect ratio measurement device and electric flu laid a solid foundation.A3515 drawing (figure 3) and related data (table 2) record the important characteristic of the most sensitive linear hall effect device;The corresponding A3516 characteristics as shown in figure 4 and table 3.
In figure 3.Linear ratio measuring hall effect device features (A3515 output)
| Table 2: linear ratio (A3515 hall effect device characteristics measurement data, When more than + 250 gauss measurements |
|||||
|---|---|---|---|---|---|
| tag | VCC (v) |
VOQ (v) |
The sensitivity (mV/G) |
nonlinearity (%) |
Degree of symmetry (%) |
| circular | 4.500 | 2.217 | 4.450 | 0.1 or less | 99.9 |
| A square | 5.000 | 2.463 | 5.014 | 0.2 or less | 99.9 |
| triangle | 5.500 | 2.710 | 5.704 | 0.1 or less | 99.7 |
| Table 3: ratio linear hall effect device characteristics measurement data (A3516), When more than + 500 gauss measurements |
|||||
|---|---|---|---|---|---|
| tag | VCC (v) |
VOQ (v) |
The sensitivity (mV/G) |
nonlinearity (%) |
Degree of symmetry (%) |
| circular | 4.500 | 2.232 | 2.149 | 0.1 or less | 99.9 |
| A square | 5.000 | 2.475 | 2.481 | 0.1 or less | 99.6 |
| triangle | 5.500 | 2.723 | 2.820 | 0.1 or less | 99.9 |
At present, although the "calibration" linear hall effect IC sales very little, but is still a great circuit to set up and magnetic parameters measurement system, and improve the ratio measurement IC performance, features and limitations of special point.
Sensor sensitivity
A3515 and A3516 are the main differences between the magnetic sensitivity.Table 2 and table 3 lists the depicted in figure 3 and figure 4 two specific sensor IC of nominal data.Sensitivity to each number of millivolt gaussian (mV/G) said.In the table lists the three voltage;However, most design USES a fixed low cost 5 V voltage chip to ensure stability.Rating of the two linear hall effect device (sensitivity and available range), as follows (VCC= 5 V) :
- A3515
- Sensitivity: 5.0 mV/G
- Scope: p + 400 G (+ / - 2.0 V or higher)
- A3516
- Sensitivity: 2.5 mV/G
- Scope: p + 800 G (+ / - 2.0 V or higher)
Linearity and symmetry
From these drawings (figures 3 and 4) clear: linearity and symmetry (static (or zero) the slope of the voltage deviation) are not crucial design result, because for A3515, both are less than 0.3%.These drawing record + 400 G (A3515), and + 800 G (A3516), for the two types of devices, the output voltage swing is + / - 2.0 V or higher.
The linear current range
According to the approximation method, the use of the scope and formula of each turn flux in front of the actual current limit value is deduced a maximum magnetic coupling (" close ") :
- Present A3515: p + 400 G 6.9 G/A material plus or minus 58 A
- Present A3516: p + 800 G 6.9 G/A material + 116 A
Based on the description of the previous, current value more than material 115 amps, need to reduce the magnetic coupling, bypass high current (i.e., will be part of the total amount through the annular coil), or you need to take effective circuit "desensitization" other methods.For "plug-in" electric measuring flu, there are many applications growing, especially for high intensity current (> 100 A).Under the condition of the current value, low value of resistance (< 1 m Ω) and heat dissipation considerable power, and the "non-inductive resistance increase costs.i.2R lossDo notAvoid;500 m Ω and 200 A loss of measuring resistance of 20 watts.Clearly, the designers want to avoid this situation.However, the choice of low cost almost no (or not).[Editor's note: Allegro ™ACS75x current sensor IC seriesHas been launched, it is suitable for current range of plus or minus 200 A.]
The linear ratio measuring hall effect IC
Figure 5 shows the contains dynamic is ac/dc offset to eliminate the latest linear hall effect device.Hall element is a "single", with the symbol (Χ) identification.In material 170 kHz frequency, current sensor IC from 0 ° direction (down) to the path of the 90 ° switch (through the hall plate).That rules out most of the factors associated with early migration resistance (gradient leads to the unbalanced dc, the difference of geometry, piezoresistive effect, etc.).Using low pass filter and sampling keeping circuit reduction feed to linear hall-effect sensor IC output ratio measurement signal.
Figure 5.With dynamic orthogonal offset to eliminate the linear hall effect sensors
For the linear hall effect IC power supply
Although the power requirement of the linear hall effect device is small, but also need external power supply.There must be a stable power supply, voltage stability is good;And with a fixed voltage IC stabilizer (usually a 5 V), the design problem easy to solve (not very much money).Linear sensor IC specified maximum power supply current for 10 mA, or less voltage 5 V (typical values material 7 mA).Low cost easily from the power system voltage chip which can adjust the board "down".
Table 4 lists the new linear ratio measurement sensor IC absolute maximum absolute value.
| Table 4: maximum absolute value (Ta.= 25 °) |
|
|---|---|
| features | Rated power |
| The power supply voltage, VCC | 8.0 V |
| The output voltage, VThe OUT | 8.0 V |
| Output current, IThe OUT | 10 mA, |
| The magnetic flux density, B | unlimited |
| Encapsulation power, PD | 600 mW * |
| * 'UA packaging rating of 183 ° C/W.[Editor's note: rating for 184.] | |
More than the prescribed limit operation may affect the operation and performance of the device, or harm (sacrifice) circuit and/or system reliability, thus (absolute) is not recommended for such operation.
The biggest power supply voltage- belt deviation linear hall effect device can eliminate the latest generation of (A3506, etc.) in the above supply voltage operation.These new linear IC improves the maximum limit, see table 4.
The maximum output voltage- see table 4;However, it is important to note that the voltage output connection could not be higher than the supply voltage or below ground voltage IC.This hall sensor IC reliability may be at risk and/or affect the system reliability.
The largest output current- the latest linear hall effect device of current is higher than previous device of the current.Typical applications, however, rarely involve more than the maximum of 10 mA, listed in table 4, even more than the percentage of the insignificant.For today's analog or conversion circuit, the high impedance input (usually)microampsInstead of milliamperes hall sensor IC output current.
The maximum magnetic flux density- more than the hall effect IC linear range of the magnetic fieldneitherHarm nor destroy devices.Exceed the available range of magnetic field, however, will force the output into the saturation state (and nonlinear operation), and won't damage the hall effect device.
The power consumption of the encapsulation- the largest packaging power consumption limits based on safe and reliable operations of junction temperature.According to the thermal resistance (below and Ta.Maximum power = + 25 ° C) on the use of two types of packaging.
- "U" encapsulation: RTheta JA(P = 183 ° C/WD= 683 mW)
[Editor's note: RTheta JARated power 184 is correct.] - "UA" encapsulation: RTheta JA(P = 206 ° C/WD= 606 mW)
[Editor's note: RTheta JARated power 165 is correct.]
Recommended maximum junction temperature of 150 ° [Editor's note: now is as high as 165 ° C.] this loss is equal to the temperaturezero.However, the latest linear devices allow up to 200 ° C of non-recurring (i.e., instantaneous) offset (ambient temperature Ta.170 ° C or less).
Internal power (PD) contains two factors: (a) hall effect device power supply (ICC* VCCIC power output () and (b) IThe OUT* VOUT (SAT)).Usually, the power restrain output loss (b) (a), and for 5 V operation, usually for 40 mW or less power loss.40 mW or less loss of power, the device junction temperature than ambient temperature (TJT or lessa.+ [PD* RTheta JARising]) material 8 ° C.
Internal power (usually)notHall effect device limiting factor, but the designer should understand the device the basic results of loss of power and its relationship with evaluation sensor IC junction temperature.The reliability of IC (and system) and all components of the system with the temperature of the inverse correlation.Around for any temperature and junction temperature is higher, the lower life expectancy and reliability of the system.
Special linear hall effect device parameters
Electric flu test application need to focus on a number of different linear hall effect device features, behind will briefly describe these parameters.Later, will focus from symmetry, temperature effect, linearity, accuracy of specific expression of many features and parameters.
The output voltage- as I mentioned earlier, ratio measurement with linear hall sensor IC provides current of induction and magnetic field is proportional to the output voltage, as shown in figure 2.When guarantee limit value, the output regulation of irrigation and the current + 1 mA.According to figure 2, 3, and 4, the available range of p + / - 2.0 V, 5 V power supply.As mentioned earlier, there is no magnetic field (or induction current), static output voltage of 1/2 power supply voltage.Stable and well regulated power supply is vital for normal operation, otherwise, the output voltage fluctuation of any changes as the power supply.[Editor's note: see the latest performance characteristicsAllegro selection guide.]
With a hall effect sensor IC circuit load- linear hall effect device for load sensing conductor is not created."Disconnect", "insert" technology is the basis of being around the sensor conductor to form a "toroid.Around the conductor to form a soft iron ring, rather than to traverse through the toroid (FIG. 6 a and 6 b).Could be don't need to disconnect any conductor in the power system, and electrical flu test (" disconnect "toroid as shown in figure 6 c).
Figure 6 A. Circular electric flu test application (< 15 A)
Figure 6 b. Circular electric flu test application (> 15 A)
Figure 6 c. "no disconnect" flu test application
The current overload tolerance- as mentioned above, more than the linear hall effect IC range of conductor current force output into the nonlinear saturation state.The current will not damage or destroy sensor IC.However, if the conductor is overheating, constant extreme overload current will cause a fire or safety hazard, and cause danger.
Hall effect current sensor response time- check using hall effect device technology and some of the toroidal coil electricity flu tested, can understand a wide range of sensor IC response time.Most of these response time (including amplifiers) in 7 ms material to material 15 ms range, other below or above the threshold.Test (usually) specified di/dt = 100 A/ms;Linear current range from fairly low (< 5 A) to limit value (> 20000 A).Obviously, 20 kA this kind of device is expensive, and do not use any low cost toroidal coil technology.
Hall effect sensor IC bandwidth- most of today's linear hall effect IC 20 kHz bandwidth available for p.On the frequency, the signal voltage change is very small.However, slightly lower frequency, phase shift of the obvious becomes apparent.Between different IC and supplier has some obvious changes, but when more than 20 kHz material attenuation is very steep.Despite all the linear hall effect device - 3 dB attenuation cut-off frequency, but 20 kHz to 25 kHz is a valid approximation.
The typical oscilloscope drawing shows the hall sensor IC signal frequency effect.From dc to 500 Hz (figure 7), there are no identifiable phase shift.At the top of the signal for the hall effect device voltage, lower trajectory for winding current (coil).
Figure 7.The V 500 HzThe OUT(upper) to the IThe IN(bottom)
Input rate of 10 kHz, phase shift become apparent (figure 8), obviously when 20 kHz (figure 9).Note: in a toroidal coil with gap in 20 test coils;Three drawing voltage ratio is not the same.Other intermediate graphics display similar phase shift, but not including due to space limitations.[Editor's note: limit refers to the publication original narrow.]
Figure 8.V to 10 kHzThe OUT(upper) to the IThe IN(bottom)
In figure 9.20 kHz 时的 VThe OUT(upper) to the IThe IN(bottom)
Moreover, it is important to note that the bandwidth limitations associated with linear sensor IC.In the operating frequency range, magnetism (and inductive coupling) is definitely not the bandwidth constraints.
Obviously, due to the bandwidth limitations, hall sensor IC can't work in normal or hear frequency (> 20 kHz) sensor using power OSFET or high power IGBT PWM circuit, but the linear hall effect device for dc and main power supply is feasible.
Response of the linear hall effect device for power applications- the system designer faces more and more demanding power "budget", and seek to save current and power technology.Batteries and battery "standby" design is of particular concern, so need detailed check any methods to cut power.
There is a cycle technology with short interval, turning on the power supply and then turn off the power supply at a relatively long period, which can activate the sensor IC (regular).Average power related to the work cycle.As a result,对于低工作周期的应用，消耗的功率可大幅减少。固定电压 IC 稳压器（带有“启用”输入）是切换霍尔效应器件电源和降低平均功率的非常可行的电路技术。
Linear hall effect IC obviously, the time required to provide a stable available signal is very important, so the linear hall effect device of two different evaluation, to make sure they add electric response characteristics.These two devices show different properties, oscilloscope picture depicts the will power when applied to linear components of dynamic working condition.The drawing contains 5% of the window, used to compare the voltage to reach the final numerical signal set.
With the use of orthogonal hall effect device compared to the last generation device, the latest linear hall effect device (orthogonal offset elimination) with dynamic response is slow.Earlier in the series (A3506, etc.) in less than 1 ms fell to 95% of the final voltage (see figure 10), need about 15 ms (see figure 11) to reach the final values.Obvious tradeoff choice: speed relative to the electric signal when the voltage accuracy and resolution
Figure 10.a.3506 功率提高 (0.2 µs/div.)
Figure 11.a.3506 功率提高 (2.0 µs/div.)
According to new devices (A3515 and A3516) slower response (material (including 25 s to 95% or more, for the final stable voltage level, for the material (including 40 s).The drawing reveals the performance relative to the response speed and basic balance of power saving potential.
Figure 12.a.3515 加电(5.0 µs/div.)
Linear hall sensor devices/toroid magnetic hysteresis- test under the condition of plus or minus 6 A, induction generate obvious oscillation output voltage signal, suggesting that involves any error is very small hysteresis (material for linear hall effect device (A3516) and has A gap toroidal coil, error of 1%).Linear hall sensor IC does not display the hysteresis, which is its inherent properties.However, different grooved ring coil () and different magnetic materials may have different hysteresis performance.
Actual measuring voltage differential in the range of 16 mV to 22 mV material, material change > 2.1 V.When using ferrite core, magnetic hysteresis is a small problem, but the other core (iron powder, for example) may show different features.
Therefore, the concrete circular coil and a comprehensive and thorough evaluation related linear sensor IC is very wise advice, and recommended.
Saturated iron core (annular coil)- iron core saturation usually is not a problem.To use enough number of turns hall effect device output voltage drive to nearly full range (maximum design current) of the current sensor application design,First of all,The sensor IC induction into a saturated state.In order to obtain the best accuracy, using the number of turns of the output voltage should be transition induction to (happen) don't make sensor IC saturation (described later).
Zero in the- for the linear hall effect sensor IC, zero pay the equivalent of the zero magnetic field (B = 0, 0, no induction flux field).Zero magnetic field, the hall effect device output voltage is equal to 1/2 (i.e., static output voltage) power supply voltage.
Broadband noise output of a linear hall effect device- it doesn't matter the linear hall effect IC broadband noise, its value is related to the selected device.For the latest stable linear hall effect IC series, the technical parameters of test as follows:
- B = 0
- BW = 10 Hz to 10 kHz
- i.The OUT1 mA or less
For linear device two series, the typical equivalent input noise voltage (Vn) values for:
- A3506, A3507, A3508:125 mV
- A3515, A3516:400 mV
Assume these the lowest sensitivity of hall effect device is 2.5 mV/G, and magnetic flux intensity is very low can't be accurately measuring (described later), so, the consequences of broadband noise (usually) is a very small problem.Other factors (especially) with the static output voltage temperature drift is more important.
The system temperature- this is the key factor to consider, it is necessary to well understand and correctly specified temperature range (no big margin).Control the important design elements to achieve reasonable accuracy.Note: open loop designCan'tEasily solve the small current changes.Material 1% of iron core hysteresis can be ruled out the small current change, and do not need to consider the linear hall effect device output parameters and its relationship with performance caused by the other (and worse) temperature effect.
Static output voltage (dc offset)- in essence, ratio measurement of linear hall IC from rated dc offset and its static output voltage (i.e., 1/2) power supply voltage offset.Because of the lack of system calibration, or "lookup table alone, really affect the dc parameters using linear hall IC of all electricity flu the accuracy of the measurement system.See figure 3 and 4, as well as in table 2 and 3, the dc offset (VOQThe importance of or static output voltage).
The latest ratio stipulated measuring hall effect sensor IC static dc output voltage limit for 1/2 + / - 0.2 V power supply voltage [Editor's note: see the appendix.].Using the linear hall effect IC, in hall effect device operating temperature within the scope of the static output voltage drift of plus or minus 10 gaussian.
Static voltage is an important aspect of its tolerance limit.Given the current specification is + / - 0.2 V [Editor's note: see the appendix.] from the nominal value, it will translate into + / - 8% of the maximum error, and no temperature effect caused by the (A3515/3516).Obviously, the potential error factors are difficult to overcome constraints, if accurate voltage is the precondition that the performance of the system, you must consider this factor.
Adjust the voltage to 2.5 V nominal voltage, this approach can be used to compensate the dc output voltage, static but this will affect the sensitivity, and does not allow any relevant deviation in production.According to figure 3 and 4, higher power supply voltage will compensate the low static output voltage, reduce the power supply voltage will compensate the high voltage static.However, such a negative influence on the sensitivity of compensation, will offset the positive aspects of static voltage "zero".
Because of the sensitivity of the linear devices latest specification includes the + / - 10% tolerance, and no temperature effect, so the "zero" static output voltage (2.5 V) to avoid static output voltage error of plus or minus 8% seems to quite absurd.
Initial linear device for "high quality", the dc drift is equal to + 20 gauss, for "limited" temperature components, drift scope to plus or minus 50 gaussian.And previous IC static output voltage tolerance range migration to eliminate the latest IC wider than the belt.
This prevents the design in a wide temperature range operation ability to accurate and precise line sexy measurement system.Design the required electrical measuring flu close tolerances must be met and wants to coordinate any associated with the static output voltage (number) and drift problems, these problems in the chapter "the accuracy of the open-loop linear hall sensor IC" in detail.
Using the above mentioned relationship between drift, the maximum static output voltage drift bias can be very approximate.These calculations based on linear sensitivity (nominal) :
- A3515: plus or minus 10 G x 5.0 mV/G material + 50 mV
- A3516: plus or minus 10 G x 2.5 mV/G material + 25 mV
- A3506: plus or minus 20 G x 2.5 mV/G material + 50 mV
- A3507:35 G + x 2.5 mV/G material + 87 mV
- A3508: plus or minus 50 G x 2.5 mV/G material + 125 mV
In essence, if static voltage drift is an important standard, and the maximum sensitivity is not the primary consideration, this list will be A3516 established linear device is first selection.In electric flu test applications, the need to double the number of turns (relative to the A3515) to obtain the same voltage swing.
For full range voltage swing (+ / - 2.0 V or higher), A3516 maximum error is plus or minus 1.3% or less, but the static voltage drift is always < + 3 G (for A3516 for material plus or minus 7.5 mV).The error factors depends on the temperature;As a result,应采用足够匝数将输出驱至接近满量程。这样会将温度相关静态输出电压漂移的整体效应减少到最低程度。因此，由于 ΔVOQError percentage is lower,strongSuggest that nearly full range of operation.
The temperature of the sensitivity of sensor IC- the front have described two kinds of new linear nominal sensitivity of the device (and range).However, there is no regulation circuit of tolerance.i.C 有不同的标称灵敏度；然而，温度相关最大漂移是相同的。在此重述灵敏度和范围，并增加公差，从而得出下述霍尔效应 IC 参数和器件温度漂移：
- A3515: sensitivity, 5.0 mV/G + / - 10%
- Δ sensitivity (Δ T), Ta.= Max - 2.5% (min), (typ) + 2.5%, + 7.5% (Max)
- Δ sensitivity (Δ T), Ta.= Min, - 9.0% (Min), 1.3% (typ) + 1.0% (Max)
- Scope of magnetic field, p + 400 G (+ / - 2.0 V or higher)
- A3516: sensitivity, 2.5 mV/G + / - 10%
- Δ sensitivity (Δ T), Ta.= Max - 2.5% (min), (typ) + 2.5%, + 7.5% (Max)
- Δ sensitivity (Δ T), Ta.= Min, - 9.0% (Min), 1.3% (typ) + 1.0% (Max)
- Scope of magnetic field, p + 800 G (+ / - 2.0 V or higher)
- Temperature range:
- Ta.(min), and 40 ° C
- Ta.(Max) and 85 ° C or 125 ° C
In essence, the open loop linear hall effect device accuracy related to the dc offset and sensitivity can be obtained.
The accuracy of the open-loop linear hall sensor IC- in any classical reasoning, involving the node of inference are very complex.Because of increasing precision and strict measurement requirements, the following will obtain the "accuracy" and concise explanation and reliability related factors.Accuracy, repeatability, cost factors are related.
Although it is possible to define the parameters maximum value, but the impact on the accuracy of accumulation is very vague.In addition, all the worst case error may not occur at the same time.Design is more and more sensitive to the cost based on the typical device specification, which may lead to not easily reduce small failure rate (although within the scope of the permit).
Accurate description "open loop" electric flu absolute accuracy of the measurement is beyond the scope of this article.However, for elements review can provide support for analysis.
- Hysteresis (hys), material plus or minus 1%
- Static output voltage, VOQ, plus or minus 8% [Editor's note: see the appendix.]
- A3515 or A3516:2.5 V + / - 0.2 V
- Output voltage static drift, Δ VOQ, plus or minus 10 G
- A3515: plus or minus 50 mV or less
- MV A3516:25 mm or less
- Ta.= Max sensitivity, plus or minus 10%
- A3515:5.0 mV/G
- A3516:2.5 mV/G
- The sensitivity of while Δ of the following:
- Ta.= Max - 2.5% to + 7.5%
- Ta.= Min, 9.0% to + 1.0%
- Positive/negative linearity, 99.7% material
- Degree of symmetry, 99.7% material
- Broadband noise, en, including 400 V
Obviously, a part of these elements is very important to obtain accurate electricity flu test, while others are irrelevant.Fundamentally speaking, symmetry and hysteresis, linearity, and broadband noise related error of little importance.Factors related to the static voltage and sensitivity to absolutely any accurate and precision electric flu test design is of prime importance.
Associated with the static output voltage drift error depends on the scope and devices.Plus or minus 10 G (usually < + / - 5 G) drift and 10 plus 50% of the magnetic field when gaussian potential error.However, plus or minus 10 G drift in the magnetic field strength > 667 G says less than 1.5% of error.As a result,静态电压误差因素是“非线性”的，A3516 线性霍尔效应器件的输出电压摆幅大时，误差大幅度减少。
Static output voltage tolerance as a percentage (plus or minus 8% or less [Editor's note: see the appendix.]).This is according to the nominal rate measurement (1/2 = 2.5 V power supply voltage) and regulations limit is + / - 0.2 V or less predictable [Editor's note: see the appendix.].Since most linear hall sensor IC closer to the nominal value (+ / - 0.1 V or less), so the + / - 8% tolerance on behalf of a "worst case" static output voltage.
The sensitivity parameters can cause considerable potential error.However, these lists the content of worst case analysis.In addition, the relationship between the sensitivity and temperature effectHas not yet beenFully determined.Device sensitivity and temperature drift caused by approaching any limits, whether there is a consistent correlation between device has not yet been set.Temperature effect may be relatedzeroOr,tiny(eliminate any accumulated temperature deviation), orThe cumulativeFurther tolerance (temperature).
According to the published parameters and restrictions, open loop electric flu test design is not easy to expected results below material plus or minus 10% to plus or minus 15%.However, in according to the test data (A3515/16) review of the latest drawing, improve the measurement accuracy of the forecast (absolute) increased.
Two drawing (figure 13 and 15) represents a VOQRelative to temperature.+ 25 ° C data record A3515 the minimum value of 2.468 V.The maximum value of 2.512 V.A3516的范围为最小值 2.464 V 至最大值 2.501 V。这个范围比规定范围严格得多。IC 的 -3 西格玛极限为：2.457 V (A3515) 和 2.462 V (A3516)。+3 西格玛极限为 2.520 V (A3515) 和 2.509 V (A3516)，在这些线性器件静态输出电压的发布公差 ±8% 范围内，这些电压值可以很好地转换 [Editor's note: see the appendix.].
A3515 data provided is as follows:
| VOQ(unit: v) , VCC= 5 V |
||||
|---|---|---|---|---|
| The environment temperature | - 40 ° C | 25 ° c. | 85 ° c. | 150 ° c. |
| - 3 sigma | 2.448 | 2.457 | 2.463 | 2.472 |
| The minimum value | 2.461 | 2.468 | 2.473 | 2.481 |
| The average | 2.487 | 2.489 | 2.493 | 2.501 |
| The maximum | 2.517 | 2.512 | 2.520 | 2.530 |
| + 3 sigma | 2.525 | 2.520 | 2.523 | 2.531 |
| VOQ(v) , as a percentage of numerical drift 25 ° C |
||||
|---|---|---|---|---|
| The environment temperature | - 40 ° C | 25 ° c. | 85 ° c. | 150 ° c. |
| - 3 sigma | 4.04 | 0.00 | 1.15 | 1.54 |
| The minimum value | 2.90 | 0.00 | 0.60 | 0.60 |
| The average | 0.59 | 0.00 | 0.74 | 2.38 |
| The maximum | 2.60 | 0.00 | 2.40 | 5.50 |
| + 3 sigma | 2.86 | 0.00 | 2.63 | 6.31 |
A3516 data provided is as follows:
| VOQ(unit: v) , VCC= 5 V |
||||
|---|---|---|---|---|
| The environment temperature | - 40 ° C | 25 ° c. | 85 ° c. | 150 ° c. |
| - 3 sigma | 2.454 | 2.462 | 2.462 | 2.466 |
| The minimum value | 2.458 | 2.464 | 2.467 | 2.472 |
| The average | 2.484 | 2.485 | 2.483 | 2.485 |
| The maximum | 2.503 | 2.501 | 2.498 | 2.499 |
| + 3 sigma | 2.514 | 2.509 | 2.504 | 2.504 |
| VOQ(v) , as a percentage of numerical drift 25 ° C |
||||
|---|---|---|---|---|
| The environment temperature | - 40 ° C | 25 ° c. | 85 ° c. | 150 ° c. |
| - 3 sigma | 3.97 | 0.00 | 3.36 | 5.13 |
| The minimum value | 3.60 | 0.00 | 1.60 | 2.90 |
| The average | 0.12 | 0.00 | 0.14 | 0.56 |
| The maximum | 3.20 | 0.00 | 3.08 | 5.70 |
| + 3 sigma | 4.22 | 0.00 | 3.60 | 6.25 |
Δ VOQRelative to the temperature data and drawing record than the limit, plus or minus 10% (before listed in millivolts) has better performance.Figure 14 and 16 VOQDrift in the range, and at any temperature of about 25 ° C + narrow range, drift is very small.Obviously, the temperature affect the output voltage drift tolerance range.
Because of these characteristics of graphics and data needs to be in the hall effect device technology parameter range, so it is strongly recommended that serious consideration can achieve accuracy (especially temperature range is limited).Fundamentally speaking, is not adopted to the calibration and/or complementary method to acquire single digits (< 10%), the accuracy of the temperature effect is the primary factor.
Figure 13.VOQRelative to the temperature (A3515)
Figure 14.Δ VOQRelative to the temperature (A3515)
Figure 15.VOQRelative to the temperature (A3516)
Figure 16.Δ VOQRelative to the temperature (A3516)
The influence of sensitivity for accuracy- the sensitivity of the drawing and data to confirm the new linear hall effect device in issue within the limits of, and depicts the another factor to solve the problem of accuracy (although is the secondary factor).Device sensitivity and its correlation with the temperature change is conservative, though no extreme test allowance.Figure 17 to 20 depicts the sensitivity data.
A3515 data provided is as follows:
| Sensitivity (unit: mV/G) | ||||
|---|---|---|---|---|
| The environment temperature | - 40 ° C | 25 ° c. | 85 ° c. | 150 ° c. |
| - 3 sigma | 4.408 | 4.683 | 4.795 | 4.842 |
| The minimum value | 4.454 | 4.793 | 4.930 | 4.927 |
| The average | 4.761 | 4.988 | 5.109 | 5.121 |
| The maximum | 5.181 | 5.316 | 5.392 | 5.359 |
| + 3 sigma | 5.113 | 5.293 | 5.423 | 5.400 |
| The sensitivity Is the value of 25 ° C when drift percentage |
||||
|---|---|---|---|---|
| The environment temperature | - 40 ° C | 25 ° c. | 85 ° c. | 150 ° c. |
| - 3 sigma | 7.6 | 0.0 | 0.1 | 0.7 |
| The minimum value | 7.1 | 0.0 | 0.9 | 1.0 |
| The average | 4.7 | 0.0 | 2.3 | 2.5 |
| The maximum | 2.5 | 0.0 | 3.7 | 4.4 |
| + 3 sigma | 1.9 | 0.0 | 4.6 | 5.8 |
A3516 data showed similar properties:
| Sensitivity (unit: mV/G) | ||||
|---|---|---|---|---|
| The environment temperature | - 40 ° C | 25 ° c. | 85 ° c. | 150 ° c. |
| - 3 sigma | 2.174 | 2.313 | 2.393 | 2.410 |
| The minimum value | 2.263 | 2.401 | 2.465 | 2.476 |
| The average | 2.340 | 2.457 | 2.530 | 2.528 |
| The maximum | 2.586 | 2.700 | 2.758 | 2.728 |
| + 3 sigma | 2.506 | 2.600 | 2.667 | 2.646 |
| The sensitivity Is the value of 25 ° C when drift percentage |
||||
|---|---|---|---|---|
| The environment temperature | - 40 ° C | 25 ° c. | 85 ° c. | 150 ° c. |
| - 3 sigma | 7.1 | 0.0 | 1.1 | 0.1 |
| The minimum value | 6.8 | 0.0 | 2.0 | 0.9 |
| The average | 5.0 | 0.0 | 2.7 | 2.6 |
| The maximum | 4.0 | 0.0 | 3.7 | 4.3 |
| + 3 sigma | 2.9 | 0.0 | 4.2 | 5.3 |
Figure 17.The sensitivityRelative to the temperature (A3515)
Figure 18.Δ sensitivity relative to temperature (A3515)
Figure 19.The sensitivityRelative to the temperature (A3516)
Figure 20.Δ sensitivity relative to temperature (A3516)
Obviously, the data and drawing didn't reflect ratio measures the overall distribution of linear hall sensor IC.For the deep understanding of the accuracy is to illustrate the basic and necessary conditions, so as to coordinate the hall effect device with electric flu can reach the limits of the measurement precision, but it is suggested that any definite constraint conditions.In the end, the application of technology innovation, and thoughtful circuit design decision open loop hall effect is the core of electric measuring flu constraints.
Calibration and compensation,Flu - through electricity design to make open loop measurement accuracy is lower than plus or minus 10%, should consider the alternative."Hardware" calibration and/or compensation is expensive and complicated choice, so for most of the design should be ignored.
Although the use of a comparator (or more) comparison calibration or compensation to establish jump point is feasible, but for temperature and static voltage, realize the full range of linear operation is still a difficult task.Comparator can provide discrete current signal, over current, normal operation, etc.), and a practical accuracy, but it can't (easily) to distinguish the small current changes.
Software is increasingly expanding hall effect device electric flu measurement accuracy of the solution.Often, software solutions involving micro-controller, including Ps, or computer, and software calibration/compensation plan.
Because of the linearity of the linear hall effect device, symmetry and ratio measurement for material 100%, so the error factors () in the very great degree can be ignored.If the system needs a wider operating range, the temperature range is the determining factor.However, narrow temperature range of benign environment can reduce the design difficulty.Using the software (and including C/P) (including development lookup table, need to measure and store the data points, for each current sensor IC to provide acceptable (and separate calibration technology.The (usually) involves the following calibration/compensation step:
- Measurement and storage of VOQ(zero current),
- Measurement and storage (specific) current point,
- With VOQAnd data sensitivity, as well as
- Measurement/storage temperature drift (if required).
Determine the current electricity at ordinary times, need to use "find" data, in order to use storage VOQCurrent value and sensitivity data calculation.
- Measuring VThe OUTAnd calculate the current value as well
- Measuring system and compensate the temperature drift effect (if the system requirements).
In essence, "find" in front of the corresponding table have been mentioned in the "calibration" linear hall effect device.The software/lookup table method can easily achieve < + / - 10% accuracy, its limit value (about material plus or minus 1%) could be affected by the limitation of various factors, including software development, the necessary calibration and compensation (including equipment), and increase the accuracy of cost and time.
Clearly, nonvolatile memory data storage required for parameter determination, also need special initial calibration procedures.Lookup table static voltage compensation, sensitivity, and the change of temperature effect factors.Can use software calibration and compensation technology, will be associated with these factors system accuracy of potential error to a minimum.Although this seems complicated and expensive, but other than using low cost solutions May 8 (including C solution is more complex and more expensive.
Hall effect sensor IC classification- although this method may enhance device output parameters;But so far only conform to the published data table limits of linear device sales.Others provide "value-added" classification scheme, but this procedure and the service is neither common nor cheap.In spite of this, some clients choose through external detection, classification and selection according to the specific devices strictly limit the design of the linear hall effect device to solve the difficult problem.Obviously, pre-classifying hall effect device IC availability of any improvement brought the flu test design can give clear advantage, and "classified" hall effect device availability may change.
The size and form of the sensor component- because of different sizes can be obtained toroid choice (Eastern Components, Inc.), so we can't determine the typical size.To suit the hall effect device packaging, with special cutting slots in coil.Figure 21展示了一个用于六个不同电流范围的基本配置（感测的额定峰值电流为：1 A、3 A、5 A、8 A、10 A 和 100 A）。长度、高度和宽度有些许变化，最大的版本测量结果是长度 0.950"、高度 1.025"、宽度 0.500"；所有版本为 PCB 通孔形式。
Figure 21.Corresponding IC hall sensor component
The cost of electricity "subsystem" flu test- determine on the basis of the linear hall effect IC current sensor related costs, almost as difficult as various problems involving system accuracy.Necessary components (linear hall effect device and grooved ring coil) is easy to determine the cost of figure 21 depicted in the complete component material starting price is $8.00 (number: 1000).[Editor's note: valuation of $1997.]
< slotted core cost usually is $1.00 (even a modest is no exception), the cost of the linear hall effect sensor IC range is $2.50 and < < $3.25 (1 000).The price span reflects all kinds of hall sensor IC and different temperature range.Obviously, the higher the total, the unit cost reduction, for mass production, the sensor IC/toroid comprehensive cost is easy to fall below $3.00.From the core into iron powder with the "casting" gap toroidal coil, can significantly reduce the total cost.Iron core is different from that of the $0.80 to $0.85, a similar number of iron powder core material cost is $0.20 to $0.25.
According to the design requirements of each individual, however, the maintenance time, other factors such as software programming, assembly work, there will be a big change.Obviously, the temperature of each system, resolution and accuracy is prerequisite to affect system costs.Develop and implement wide temperature range, high resolution and very accurate design, the feeling of the required fees and only test the excess current expenses have great different.Over current fault detection applications available tolerance range is very large (about + / - 20%), but this doesn't guarantee to realize precise temperature range full design requirements of any software to "find", the strict evaluation device and temperature.
Therefore, only able to identify the core parts (and component figure 21).Creation, system design and software engineering and other related expenses is not using the linear hall effect IC electrical flu measuring range.
Protection of high power electronic devices
Figure 22 is the high power IGBT power flu detection and protection of the classic examples.For ac induction motor or need full bridge or three and a half bridge drive (e.g., three-phase brushless permanent magnet dc motor) of the other power circuit, the figure and can be adjustable speed drive (ASD) single phase.This configuration can detect the power rail (upper current sensor) the excess current.This may be because of under the condition of the activation of corresponding IGBT, power supply rail of short circuit, or output short circuit.Short circuit output low or high output with the same "leg" opposite position output arbitrary combination, can cause the system to produce (unsafe) over current fault.
Figure 22.'the whole bridge with current sensor IC
Sensor (center) as a choice, and winding in series of linear sensor IC can detect short circuit load, and monitor the actual coil current.Two locations in the current sensor IC should be ruled out fire and safety hazards, and to protect any personnel);And the "off" circuit can prevent harm to the power output (if the external fault, such as improper equipment maintenance flow).Obviously, and the overall circuit response speed (closing time) to protect the system and to provide security is very important.
Summary and outlook
For open loop electric flu is the linear hall effect sensor IC developing and expanding.At present, the available equipment are all excellent linear devices than they used to, and in the design, processing, packaging, testing progress continuously, etc.As mentioned earlier, if you want to make a design, development and implementation of the system work in a wide temperature range with reliable accuracy of single digits, today's tolerance and temperature drift of hall effect device proposed the challenge to designers.
Hall effect device performance and temperature stability is expected to progress, as well as the integration more and other advances, and will make linear hall effect device is more suitable for higher resolution electric measuring flu.
Future linear device may allow the hall effect device after encapsulation, the sensor IC programming.This will allow the user to adjust the gain (sensitivity), static calibration output voltage (VOQ) and to compensate temperature change.Obviously, this involves the circuit design and test more complex technology innovation.However, application of this kind of hall sensor IC opportunity to geometric progression growth.
Since the late 1960 s after implementing integration, hall effect sensor IC undergone a revolutionary change.Along with the further development and improvement, for the new linear hall effect device application is expected to expand and increase, in order to meet the future demand for many emerging in the power electronics system.
Thank you
A sign of a linear hall effect current sensor [Editor's note: the application of the as shown in figure 22.Χ logo is driven magnetic standard said.] by雷竞技竞猜下载 Allegro MicroSystems former employees of Raymond Dewey creation.At present, for the use of hall effect current sensor technology, there is no standard or accepted graphic symbols.
The resources
Courses: p. Emerald, Baltimore, Maryland, power system, the world in 1997, the sixth chapter, PCIM (power conversion and intelligent motion) institute of power electronics, electric measuring principle of influenza "application for power conversion and motion system of the open loop electric measuring flu".And this one-day career progress course chapters of contributors.
Seminar: p. Emerald and Joe Gilbert, long beach, California, in 1995, the power system, "used in motion control and positioning the application of integrated hall effect sensor".
The appendix
Because this article was written in 1997 December, now A3515 and A3516 ratio measuring linear hall effect sensor IC has been replaced by the A132x series.Can from Allegro websiteA1324-5-6Get information about the new series.
In addition, after the first publication on A3515 and A3516 ratio measure the technical parameters of the linear hall effect sensor IC changed.In April 1998, the new strict static output voltage limit changes from the original 2.5 V + / - 0.2 V + / - 0.075 V to 2.5 V.In addition to static output voltage limit upgrade, effective linear current range can be achieved by widening gap annular coil (slot), expand to desensitization "magnetic coupling".
According to called "static output voltage (dc offset)" section, technical parameters of original ratio measurement output is usually listed as 2.5 V.The limiting value of 2.3 V (minimum) and 2.7 V (Max), V device working temperature scopeCC= 5 V.The improvement ratio is used to measure the linear hall effect sensor IC system can achieve the accuracy (see called "open loop linear hall sensor IC accuracy" section below).
As mentioned above, the paper gives the following output static voltage limit:
VOQ...2.48 V to 2.52 V (+ / - 8%)
Upgrade technical parameters shows that the output voltage static limit is as follows:
VOQ...2.425 V to 2.575 V (+ / - 3%)
The strict technical specifications significantly increased the proportion by the linear hall effect sensor IC to achieve a more accurate measurement of the ability.This means that the accuracy of single design become a reality for some, particularly those temperature fluctuations limited design).
On linear current range - according to the linear current range of initial material (page 5), with a "tight" magnetic coupling (» 60 ma gap, to match the sensor encapsulation) the scope of the same:
Present A3515: p + 400 G 6.9 G/A » plus or minus 58 A
Present A3516: p + 800 G 6.9 G/A » + 116 A
By extending the slot (widen) toroid can easily realize the magnetic coupling "desensitization."Magnetic coupling desensitization groove increased to 3 mm in the first place (material encapsulation body twice), thus reducing the magnetic flux coupling, and increases the current limit, as follows:
Present A3516: p + 800 G 3.85 G/A » + 210 A
Tests show that sensor IC shell arrangement has no effect on magnetic coupling.Will "calibration" placed in the center, linear hall effect sensor IC shell shell when placed in the slot on the output signal and the output signal of the same.Because many users trying to get a higher current range, so we conducted another assessment (from Eastern Components, Inc., new ferrite toroid).
Will the toroid gap widened to 6 mm (i.e., more than the thickness of the encapsulation size 4 x), extending the scope of current limit again.The magnetic coupling of desensitization increased the maximum current limit, calculated according to the following:
Present A3516: p + 800 G 1.7 G/A » + 470 A
In different size gaps can be obtained after the toroid, need further evaluation.It should be able to provide a more complete (despite the overlap) current scope set (ceiling still unknown).In addition, other toroidal coil materials (particularly iron powder) under evaluation.
conclusion
Static output voltage tolerance make strict ratio measuring the accuracy of the linear hall effect device is better, widen the toroidal coil slot can increase the maximum current limit of the device.
In this paper, published on May 6, 1998, the international home appliance technology conference held at the Ohio state university.Reproduced with permission.
STP98-1