Powerware ST-2400S Full scale Torque Ft.-Lbs, K Ohm Shunt Resistor Torque, 64.14, 128.3, 320.7

dynamometer. The calibration torque produced is equal to the sum of the torque produced by the Torque Test Bar itself plus the torque produced by the test weight(s) – which is equal to the total weight of the test weight(s) times the horizontal distance from the center line of the dyno to the position of the test weights. For example, assume the torque of the torque test bar itself is 17 Ft.- Lbs., the total weight is 100 Lbs. and the horizontal distance is 4.00 Ft. The calibration torque value produced by this setup is equal to 417 Ft.-Lbs. ( = 4.00 Ft. * 100 Lbs. + 17 Ft.-Lbs.)

2.) Shunt Resistor: The 2400S horsepower computer has an internal shunt resistor which can be used to check the torque span calibration. The 2400S can (optionally) be equipped with a precision shunt resistor which can be used to perform a NIST (National Institute of Standards and Time) traceable torque calibration. The “torque” introduced by the shunt resistor depends on the resistance value of the shunt resistor as well as the properties of the load cell. For the NIST traceable torque calibration to be accurate, both the shunt resistor value and the load cell must have NIST traceable calibrations which should be checked periodically. A 2400S horsepower computer without the precision shunt resistor is equipped with a 1% precision 45.3 K Ohm shunt resistor (not adequate for NIST traceable calibrations) which can be used for a quick and fairly accurate check on the torque calibration and the torque sensor circuits of the 2400S. After performing the calibration of the unit using the dead weight test fixture calibration method, remove the dead weight test fixture and set the Shunt Resistor Switch to ON. The shunt resistor will produce a torque reading that is (roughly) 2/3 of the full scale torque of the unit (i.e. about 3300 Ft.-Lbs. on a 5000 Ft.-Lbs. full scale 2400S). More precise values are shown in the table below. The reading should be within +/- 2 or 3 % of the appropriate value from the table below. The tolerance derives from the +/- 1% tolerance of the 45.3 K Ohm shunt resistor plus the tolerance of the load cell (likely +/- 1 or 2 %). If the reading is not this close, you should double check the calibration and your procedure as a likely problem is indicated. If the reading is within the above limits, record its value. It can be used later for a quick check on your unit’s calibration as it should be stable over time and temperature to within +/- 0.25% or better.

Full scale Torque (Ft.-Lbs.)	45.3 K Ohm Shunt Resistor Torque
100	64.14
200	128.3
500	320.7
1,000	641.4
2,000	1283
5,000	3207
10,000	6414

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