Martel Electronics DPM742-BL - Manual (Page 3)

SCREW TERMINAL FUNCTIONS
CALIBRATION
I+ Positive current input.
I- Negative current input.
BL+ Positive power supply connection to the LED backlighting.
BL- Negative power supply connection to the LED backlighting.
The meter is supplied calibrated to read 000 for 4mA loop current and 1000 for 20mA.
CIRCUIT DIAGRAM
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To re-calibrate, place the Jumper Link across LK1. This disables the Offset adjustment to enable Span adjustment to be made first. After
Span adjustment is complete, the Jumper Link is removed and the Offset adjustment is made. The Jumper Link is then used to display one
of the decimal points if necessary.
Example to re-calibrate: Meter to read -40.0 at 4mA and 150.0 at 20mA.
1. Calculate the Span by subtracting the desired reading at 4mA from the desired reading at 20mA: 1500 - (-400) = 1900
2. Place Jumper Link Lk1 with the link header normally used to select the desired Decimal Point.
Link Lk1 is located to the left of the screw terminals.
3. Apply 16mA between the + and - screw terminals.
4. Adjust the Span potentiometer so the DPM 742-BL indicates 1900.
5. Remove Jumper Link Lk1 and place it back on the desired Decimal Point (DP1 in this case).
6. Apply 4mA between the - and + screw terminals.
7. Adjust the Offset potentiometer so the DPM 742-BL indicates the desired reading at 4mA: -40.0
8. Adjust Span and Offset as necessary for optimum accuracy. First apply 20mA and adjust Span untill
the reading is 150.0. Then apply 4mA and adjust Offset untill the reading is -40.0.
Repeat step 8 until correct readings are obtained at 4mA and at 20mA.
Offset
Span
DPM 742-BL
4-20mA Loop Powered Indicator with Backlighting
PO Box 770, Londonderry, NH 03053 1-800-821-0023
www.martelcorp.com