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PROGRAMMING AND ELECTRICAL CALIBRATION
7.5
Electrical Calibration
✶
Note. The instrument is calibrated by the company prior to despatch and an electrical calibration should only be carried
out if the accuracy of the instrument is suspect.
7.5.1
Equipment Required
a) Current source: 0 to +100
µ
A.
b) Decade resistance box (temperature input simulator): 0 to 1k5
Ω
.
c) Digital milliammeter (current output measurement): 0 to 20 mA.
✶
Note. Resistance boxes have an inherent residual resistance which may range from a few milliohms up to 1 ohm. This value
must be taken into account when simulating input levels, as should the overall tolerance of the resistors within the boxes.
7.6
Preparation
a) Switch off the supply and disconnect the sensor, temperature compensator and current output from the electronics unit
terminal block – see Fig. 3.4 or Fig. 3.5.
b) Wall Mounted Instruments
1)
Connect the microamp source '+' and '-' to terminals 1 and 3 respectively.
2)
Connect the decade box between terminals 5 and 6, with terminals 6 and 7 linked.
3)
Connect the milliameter to the retransmission output terminals.
4)
Ensure that the earth of the current source and decade box are connected to the instrument earth stud.
Panel Mounted Instruments
1)
Connect the microamp source '+' and '-' to terminals 12 and 10 respectively.
2)
Connect the decade box between terminals 7 and 8, with terminals 6 and 7 linked.
3)
Connect the milliameter to the retransmission output terminals.
4)
Ensure that the earth of the current source and decade box are connected to the instrument earth stud.
c) After either of the sections in b) above, switch on the supply and allow ten minutes for the circuits to stabilize.
d) Select the Electrical Calibration Page and proceed as in Section 7.7, following.
