ATEC 2575A Wideband Current Shunt or Precision Resistance Standard User Manual

Advanced Test Equipment Corp.
www.atecorp.com
B00-404-ATEC (2832)
Model 2575A
Wideband Current Shunt / Precision
Resistance Standard Opera
M ELITEL

CERTIFICATION

Valhalla Scientific, Inc. certifies that this instrument was thoroughly tested and inspected and found to meet published specifications when shipped from the factory. Valhalla Scientific, Inc. further certifies that its calibration measurements are traceable to the National Institute of Standards and Technology to the extent allowed by NIST’s calibration facility.

WARRANTY

The warranty period for this instrument is stated on your invoice and packing list. Please refer to these to determine appropriate warranty dates. We will repair or replace the instrument during the warranty period provided it is returned to Valhalla Scientific, Inc. freight prepaid. No other warranty is expressed or implied. We are not liable for consequential damages. Permission and a return authorization number must be obtained directly from the factory for warranty repairs. No liability will be accepted if returned without such permission. Due to continuing product refinement and due to possible parts manufacturer changes, Valhalla Scientific reserves the right to change any or all specifications without notice.

SECTION I UNPACKING AND INSTALLATION

1-1. Introduction
The Valhalla Model 2575A is an AC/DC Current Shunt that can be used as a laboratory standard for current or as a resistance standard. Also included is a built-in precision buffer amplifier with a gain of 10.000.
The 2575A offers six isolated, switch- selectable decade ranges from 2mA to 100A full scale. Each shunt is a four-terminal, non-inductive type resistance – element ensuring a flat frequency response throughout the bandwidth of the instrument.
The shunts may be forced-air cooled to minimize temperature rise and maximize thermal stability.
The full scale voltage drop at the non- amplified output terminals for the lower shunts is 200.00mV. The full scale voltage drop across the 100A shunt is 100.00mV. The 2575A provides six decades of four- terminal resistors from .0010 to 100Q. Each can be used  s a laboratory standard resistor. Each range is independently adjustable for ease of calibration.
Also included in the Model 2575A is a built-in precision buffer amplifier with a gain of 10.000. This amplifier has a frequency response from DC to 10KHz. The amplifier can also be used with external inputs by placing the range switch to EXT. Inputs should not exceed 200mV. The output of the amplifier is suitable for driving thermal transfer systems, if desired.
1-2. Initial Inspection
If the external shipping container shows evidence of damage, it should be immediately brought to the attention of the carrier and such damage noted on the bill of lading.
Unpack the instrument and retain the shipping container until the instrument has been inspected for possible damage in shipment. If shipment damage is apparent, notify the carrier and obtain authorization for repairs before returning the instrument to the factory. If the external shipping container shows evidence of damage, but the instrument shows no external damage, it may be advisable to check the performance of the unit to determine that the instrument has not sustained hidden damage.
1-3. Power Requirements
The instrument is shipped from the factory for operation at 115VAC or 230VAC 50/60 Hz. This voltage range is selectable via the rear panel switch. When 115VAC is selected, the unit will operate at line voltages from 80 to 130 volts. When 230VAC is selected, the unit will operate at line voltages from 160 to 250 volts. A ¥ Amp Slo-Blo fuse is used in the 115V position. A .125Amp Slo-Blo fuse is used in the 230V position. Refer to Table 2-3.
1-4. Installation
If the Model 2575A is to be used in the bench top configuration, installation requires only that the line cord be connected to the rear panel connector and the other end inserted into the appropriate wall receptacle. A rear panel mounted fuse provides protection for the internal circuits.
Optional brackets are available to mount the unit in a standard 19″ equipment rack, designated as Option RX3. Due to its size and center of gravity, the unit should be supported on both sides and along its entire length by the use of trays or slides. If it is to be transported while in the rack, the unit should be securely mounted to prevent upward or downward movement.
Proper ventilation must be maintained in order to assure maximum performance from your Model 2575A. Note the location of the air vents on the rear of the instrument.
A free flow of air should be provided around these vents. Performance is degraded at higher temperatures as specified in Section 2. At no time should the ambient air temperature around this instrument exceed 50°C while operating.

SECTION II SPECIFICATIONS

2-1. General
This section contains accuracy, operating and environmental specifications for the Model 2575A.
Table 2-1. Ranges and Accuracy (1 year @ 25°C +5°C)²

Range Name & Maximum Input| Shunt Value| DC Accuracy (% of Range)| AC Accuracy (% of Range)| Frequency Response
---|---|---|---|---
100A| 0.001Ω| ± 0.05%| ±0.1%| DC to 1KHz
20A| 0.01Ω| ± 0.02%| ±0.1% Ill| DC to 10KHz
2A| 0.1Ω| ± 0.02%| ±0.1%| DC to 10KHz
200mA| IΩ| ± 0.01%| ± 0.1%| DC to 10KHz
20mA| 10Ω| ± 0.01%| ± 0.1%| DC to 10KHz
2mA| 100Ω| ± 0.01%| ±0.1%| DC to 10KHz
Notes:
[1] AC accuracy is +0.5% of range above 1000Hz.
[2] Outside the specified temperature range, add +0.001% of range per °C.

Table 2-2. Amplifier Characteristics

Table 2-3. Physical Specifications

SECTION III AVAILABLE OPTIONS

3-1. General
This section lists the options available for the Model 2575A AC/DC Shunt. Standard accessories include a detachable power cord and an operation manual.
3-2. Optional Accessories
Option RX3: Rack Ears
Option RX3 is a set of rack ears that adapt the Model 2575A for installation in a standard 19″ equipment rack.
Option 1-150: Current Transformer
Option 1-150 is a clamp-on current transformer (CT) that extends the AC current measurement capability of the 2575A to 150 amps. The 1000:1 ratio is 2% accurate from 50Hz to 400Hz. The device accommodates conductors up to 2″ in diameter.
Option 1-1000: Current Transformer
Option 1-1000 is a clamp-on current transformer (CT) that extends the AC current measuring capability of the 25754 to 1000 amps. The 1000:1 ratio is 2% accurate from 50Hz to 400Hz. The device accommodates conductors up to 2″ in diameter.
Option BBL: Banana to Banana Cable
Option BBL is a 4’ shielded coaxial cable terminating in double banana connectors.
Option HC: Heavy-Duty Cable
Option HC is a 4AWG heavy-duty cable designed to connect the Valhalla Model 25554 100 amp output terminals to the Model 25754 100 amp input terminals.

SECTION IV OPERATION

4-1. General
This section of the manual contains complete operating instructions for the Model 2575A AC/DC Current Shunt. Included are control functions, connection methods, and operational precautions.
4-2. Power ON/OFF
A push-button mounted on the 2575A front panel is used to apply or remove AC line power to the instrument. Illumination of the front panel indicator confirms application of power.

The unamplified output terminals may be used regardless of whether or not the 2575A is connected to the AC line power. In this situation, however, no cooling is provided to the shunts and prolonged use of high currents should be avoided.
4-3. Front Panel
The location and function of the front panel controls is described in Table 4-1.
4-4. Rear Panel
The location and function of the rear panel controls is described in Table 4-2.
4-5. Using the 2575A to Measure Current
The following method is recommended when using the 2575A to measure AC or DC current:

1. Approximate the maximum value of current that is likely to be encountered during the test. Use this value to select a shunt of the 2575A that has a rated current that is greater than this amount.
   CAUTION!
   Shunts can be damaged by the application of currents greater than the rating of the shunt. If the amount of current to be measured is unknown, start by making connections to the 100 Amp terminals. This prevents damage to the lower shunts. Once the level has been approximated, choose the appropriate shunt and make new connections as necessary.

2. Connect the input current to the selected shunt using a gauge of wire that is appropriate to the amount of current to be measured. Heavy-duty lugs or Valhalla Option “HC” should be used when connecting to the 100 Amp terminals. Use the table below as a
   guide: Range| Recommended Wire
   ---|---
   < 2A| 20 – 22 AWG
   2A| 18 – 20 AWG
   20A| 14 – 16 AWG
   100A| 3-4 AWG

3. Select the appropriate range with the Range Selector knob.

4. Connect the measuring device (DVM, thermal transfer standard, etc.) to the amplified or unamplified output terminals as desired. The unamplified terminals may be used even if the 2575A is not plugged into the AC line.
   The full-scale output voltage of the unamplified terminals is £200mV DC or Caps. The full-scale output voltage of the amplified terminals is =2V DC or ArcGIS-
   The shunts are isolated through the selector switch. It is not necessary to remove a load connected to one range in order to connect a load to another range.
   The amplified output may drive a load of 10mA maximum.

4-6. Using the 2575A as a Resistance Standard
The Model 2575A may be used as a laboratory resistance standard. The resistor values are 0.001Ω, 0.01Ω, 0.1Ω, 1Ω, 10Ω and 100n. Four-wire resistance measurement should be made in the following manner:

1. Select the resistor to be used by referring to the markings near the terminals on the 2575A front panel.
2. Connect the current sourcing terminals of the ohmmeter to the appropriate 2575A shunt input terminals.
3. Connect the voltage sensing terminals of the ohmmeter to the 2575A Output Voltage terminals. The unamplified terminals should be used.
4. Select the working shunt with the Range Selector knob.
   The Valhalla Model 2575A is designed for use in a 4-wire resistance configuration. While it is possible to use the 2575A as a 2-wire resistor, this configuration is not specified and may produce large inaccuracies.

4-7. Using the Built-In Precision Amplifier
The Valhalla Model 2575A incorporates a precision buffer amplifier which may be used by itself or with the shunts as described above. If the amplifier is to be used by itself, the following steps should be performed:

1. Set the Range Selector knob to “EXT”.
2. Connect the input signal to the left set of “Output Voltage” terminals. These terminals double as the input terminals to the precision amplifier. The maximum input voltage should not exceed £200mV DC or Caps.
3. Connect the measuring device to the right set of “Output Voltage” terminals.  The maximum output voltage is +2V DC or ACgys. The maximum current provided by the amplifier is 10mA.

Figure 4-2. 2575A Rear Panel

SECTION V CALIBRATION

5-1. General
The Model 2575A should be calibrated at regular intervals to ensure continued accuracy. This interval may be determined by usage, however the instrument has a factory calibration interval of 12 months.
5-2. Required Test Equipment
a) Digital Voltmeter with a DC accuracy of at least 0.005% and ranges of 200mV and 2V (HP3458A or equivalent)
b) DC Voltage Source 0.001% accuracy (Valhalla 2701C or equivalent)
c) Current Calibrator with ranges of 100A, 10A, 1A, .1A, .01A and .001A (Valhalla 2555A or equivalent)
d) Precision Resistors with known values to within ±0.003%

5-3. Description of Procedure
The Valhalla Model 2575A is calibrated using a stable source of DC current (the Valhalla Model 2555A) and a highly accurate DC voltmeter. It may be noted that the accuracy of the 2555A is not as high as the 2575A. By using the current source as a transfer  standard (transfers the accuracy of the standard resistors), the shunt may be calibrated to a tolerance that nears the uncertainty of the standard resistor used. For this reason, the results of the calibration depend to a great deal upon the quality of the standard  resistors used. A typical calibration setup is shown in Figures 5-1 and 5-2.
In Figure 5-1, the current source is adjusted to produce a precise value of current by measuring the voltage drop across the standard resistor which has a known value.
For example to adjust the current source to produce exactly 100 Amps, the voltage across the .001q resistor is measured. The current source is adjusted until the reading on the voltmeter reflects that of the standard resistor (using Ohm’s Law: V=IR). The output of the current source is now a precise 100.00 Amps.
The leads are then moved as shown in Figure 5-2 to the Model 2575A 100A shunt terminals. The voltage at the output terminals is monitored with the precision voltmeter. The appropriate potentiometer is adjusted for a reading of exactly 100.00mV, indicating that the shunt is now trimmed to a precise value (i.e. 0.0010000 ohms).
5-4. DC Calibration
The calibration adjustments are made using potentiometer adjustments located inside the 2575A. One adjustment for each shunt is provided, as well as one for the buffer amplifier. Adjustments are accessed by removing the top front bezel, and the top cover. For maximum stability, the cover should be kept in place as much as is practical. ~ Potentiometer placement is shown on the board itself and on drawing number 2575-600 at the back of this manual.
Apply AC power and allow the 2575A to warm-up for at least 15 minutes in a stable environment with the covers in place before proceeding.
5-4-1. Amplifier Adjustment

1. Set the 2575A Range Selector to “EXT”.
2. Connect the DC voltage source at 100mV to the left set of “Output Voltage” terminals of the 2575A. These terminals also serve as the amplifier input terminals.
3. Connect the voltmeter to the right set of “Output Voltage” terminals.
4. Adjust RV7 until the voltmeter reads 1.00000 volt.
5. Reverse the polarity of the input voltage and balance RV7 for an equal deviation at both input polarities. Both readings must be within ±200μV.
   5-4-2. Shunt Adjustments

1. Connect the calibration equipment as shown in Figure 5-1 using the desired values shown in Table 5-1.

2. Adjust the value of the current source until the output is exactly equal to the Test Current shown in Table 5-1. This is calculated using Ohm’s Law: V=IR.
   Where:
   R = the precise value of the standard resistor
   I = the value of test current shown in Table 5-1
   V = the voltage across the standard resistor
   100 Amp Shunt Example:
   R=0.0010270Ω
   I= 100.00 amps
   V= 10270 volts
   The current source should be adjusted until the voltmeter reads 0.10270 volts. The current source has now been trimmed to produce a precise 100 amps.

3. Make the connections as shown in Figure 5-2.

4.  Adjust the appropriate potentiometer of the 2575A for a voltmeter reading of 100.00mV.

All shunts are calibrated using the same procedure as was used above for the 100 amp shunt, but the values shown in Table 5- 1 are substituted accordingly. The shunts may be calibrated in any order desired.
5-5. AC Calibration
The AC frequency response of this instrument is inherent in its design and requires no periodic adjustments. The frequency response should be checked whenever a repair is made to the amplifier or to any shunt resistor. If you should doubt the integrity of your instrument, please contact the factory.
Table 5-1. Calibration Variables

2575A Range| 2555A Range| Standard Resistor| Test Current [¹]| Adjust| DVM Reading
---|---|---|---|---|---
100A| 100A| 1Ω| 100 Amps| RV1| 100.00mV
204| 20A| 1Ω| 10 Amps| RV2| 100.00mV
24| 24| 1Ω| 1 Amp| RV3| 100.00mV
200mA|  200mA| 1Ω| 100 m Amps| RV4| 100.00mV
20mA| 20mA| 10Ω| 10 m Amps| RVS| 100.00mV
2mA| 2mA| 100Ω| 1 m Amp| RV6| 100.00mV

[¹] The test current should be verified and adjusted as necessary using the standard resistors as a reference prior to making any adjustment on the 2575A. (See Section 5-4.)

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References

• Test Equipment Rentals, Sales, Calibration | ATEC

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