Electro-Chemical Devices (ECD) SMS22 - Manual (Page 40)

Calibration
The meter is supplied calibrated to read 000 for4mA loop current and 1000 for 20mA.
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 4mAand 150.0 at 20mA.
1. Calculate the Span by subtracting the desired reading at 4mAfrom 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 theDPM742-BL indicates 1900.
5. Remove Jumper Link Lk1 and place it back on the desired Decimal Point (DP1 in this case).
6. Apply 4mAbetween the – and + screw terminals.
7. Adjust the Offset potentiometer so theDPM742-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 until the
reading is 150.0. Then apply 4mAand adjust Offset until the reading is -40.0.
Repeat step 8 until correct readings are obtained at4mAand at 20mA.
SMS-22 Page 31