9-10
9.2 Thermocouple / mV Calibration
All HiD range of isolator are designed for long term stable and trouble free operation. They have been factory
calibrated using high accuracy, periodically certified, traceable standard calibrators operating under computer
control to perform an automated Final Testing procedure and Test Data Recording. Therefore they should not
require, under normal operating circumstances, any calibration check or readjustment.
For input type or range modification, however is necessary re-calibrating the output scale to adjust to the new input
values.
9.2.1 Equipment required
In case a calibration check or readjustment is necessary the following equipment is required:
•
4 ½ digit digital multimeter
Range 20 V, resolution 1 mV, accuracy
±
0.1% or better
Range 20 mA resolution 10
µ
A, accuracy
±
0.1% or better
•
mV / Thermocouple calibrator
Range 0-100 mV, resolution 10
µ
V, accuracy
±
0.05% or better
9.2.2 Thermocouple or mV Input range modification
In case of input type changing you must configure the instrument according to the procedure given in section 5.9
In case of input range changing, the input range setting dip-switches position must be changed following the
procedure:
1) Find the required input type at the paragraphs 9.1.1 to 9.1.9 ( example TC “J” at 9.1.4).
2) Select the Zero and Span tables that better satisfy the range extension required (i.e. –210 to +1200
°
C).
3) Find on the Zero table the value closest to the one to be calibrated (i.e. 0 for a range 0 to +840
°
C) and set the
switches SW2 accordingly.
4) Find on the Span table the value closest to the one to be calibrated (i.e. +825
°
C for a range 0 to +840
°
C) and
set the switches SW2 accordingly.
5) Proceed then in calibrating the front accessible trimmers for fine adjustment output value based on input
signal range.
6) If the calibration is difficult, select on the Zero and Span tables a new range close to the previous one and
repeat the calibration procedure.
9.2.3 Thermocouple Input Range Calibration
It is well known that the thermoelectric e.m.f. of a thermocouple is the algebraic sum of all the emission of the
thermoelectric junction constituting it (usually the measuring and reference junctions).
A compensating cable must be used for the input connection and a compensation of the junction potential at the
converter’s input cable must accounted for. This reference junction compensation feature is already built in the
isolator by means of an automatic compensator consisting of an RTD that must be putted directly on the input
terminals (4-8 for channel 1 and 3-6 for channel 2) from the user.
When performing the instrument calibration the mV signal supplied by the calibrator must account for the
Reference Junction emission potential for providing the correct calibration potential in mV.
Some calibrating configuration can be used to perform the input range signal calibration:
Note:
For thermocouple type “B” follow the mV Input Range Calibration paragraph.
Summary of Contents for HiD 2000 Series
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