11
1021 Technical Manual
11
7.
R ecalibration
The instrument is calibrated before it leaves the factory and should require no further
adjustment for at least 12 months unless the circuit module or any of the calibration
determining components have been damaged.
Before considering recalibration, the customer should ensure that any apparent error in
output current is not due to inadequate measuring equipment or noise pick-up. The latter
can be misleading at low settings of output current.
The customer should also ensure that the correct equipment is available before attempting
recalibration.
There are 2 ways the 1021 can be recalibrated:
(a)
The output current can be converted to a voltage by connecting a precision resistor
across the output terminals. 3 values are required, 100, 1K and 10K ohms. The resistors
must be accurate to better than 0.01% and have a good stability under load. The 10 ohm
will dissipate 0.1 watts at 100mA and therefore must have a temperature stability good
enough to ensure that it remains within 0.01%.
The voltage across the load resistor can be measured with a high performance DVM. (50
ppm accuracy on the 1 volt DC range, and greater than 100 Megohms input).
(b)
The output current can be measured directly on a high performance DVM. (50 ppm
accuracy on 1 mA, 10 mA and 100 mA ranges).