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8 CALIBRATION
✶
Note. The instrument is calibrated by the Company prior to despatch and recalibration should be carried out:
•
Only if the instrument's accuracy is suspect and suitably calibrated test equipment is available.
•
At 12 monthly intervals for re-validation provided suitably calibrated test equipment is available.
8.1 Equipment Required
a) Decade resistance box (cell input simulator): 0 to 10KΩ (in increments of 0.1Ω), accuracy ±0.1%.
b) Decade resistance box (temperature input simulator): 0 to 1KΩ (in increments of 0.01Ω), accuracy ±0.1%.
c) Digital milliammeter (current output measurement): 0 to 20mA.
✶
Note.
•
Resistance boxes have an inherent residual resistance which may range from a few mΩ 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.
•
All test equipment must be traceable, with valid test certification.
8.2 Preparation
a) Switch off the supply and disconnect the conductivity cell, temperature compensator and current output from the instrument's
terminal blocks – see Fig. 4.4 (page 10) or Fig. 4.5 (page 11).
b) Connect the decade boxes to the appropriate terminals – see Table 8.1. Ensure the earth on the conductivity decade box is
connected to the case earth (ground) stud. Connect the milliammeter to the retransmission output terminals – see Fig 4.4
(page 10) or Fig. 4.5 (page11).
c) Switch on the supply and allow ten minutes for the circuits to stabilize.
d) Select the FACTORY SETTINGS page and carry out Section 8.3.
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