Calibration - Extech Instruments 48VTR User Manual

Calibration

Important Note: Calibration is rarely required. In addition, special equipment is
required in order to perform a calibration. The calibration procedure cannot be aborted
once the calibration parameters are accessed, therefore do not initiate the calibration
process until fully prepared and qualified to do so. It is safe, however, to scroll through
th
the 4 Menu Level to view the settings. Follow these steps only if prepared to do so.
1. Access the 4th Menu Level as described in the previous section. 'LoCA' (Low
Calibration) is the first parameter to appear.
2. Connect a Thermocouple (mV), RTD (resistance), 4-20mA, or 1-5VDC calibrator to
the controller's input terminals (depending on the controller's input type).
3. Apply the low input signal to the controller which corresponds to the range you are
using, i.e., for 4-20 mA inputs, 4 mA would now be applied to the controller.
4. Use the UP/DOWN arrows to set the display value that will correspond to a 4mA
input. For example, for a 4-20mA input to display –50 to +150, set 'LoCA' to –50.
5. Press and hold the RETURN key for at least 5 seconds and the parameter on the
display will change from 'LoCA' to 'HiCA' (High Calibration). The Low Calibration
value is now written into the controller's non-volatile memory.
6. Apply the high input signal to the controller, which corresponds, to the range you
are using. For example, for a 4-20mA input controller, apply a 20mA signal.
7. Use the UP/DOWN arrows to set the display value that will correspond to a 20mA
input. For example, for a 4-20mA input to display –50 to +150, set 'HiCA' to +150.
8. Press and hold the RETURN key for at least 5 seconds; the meter will return to
normal operation. The High Calibration value is now written into the controller's
non-volatile memory.
9. Input a signal midway between the Low and High Calibration signals previously
applied and verify that the display indicates a value midway between the high
display and the low display value. For the example above, apply 12mA (midway
between 4 and 20mA) to display +50 which is the midway point between the high
and low display values.
10. If the controller does not indicate the expected display values, re-calibrate the
instrument. If the display still does not function correctly, contact Extech
Instruments for technical support or return the instrument for repair or replacement.
20 Model 48VTR - Version 5.0 – January 2006