Measurement Computing DBK Part 2 - Manual (Page 139)

DBK Option Cards and Modules 988793 DBK65 pg. 11
Calibrating a Transducer using the “Shunt Calibration Technique”
The “shunt calibration” technique involves applying a known resistance across one leg of a transducer.
When the resistance is applied, the transducer’s output changes as it would if an actual load was applied.
Typically, transducers with internal amplifiers already have a built-in shunt calibration resistor. The shunt
calibration resistor can be activated via the DBK65 by use of its rear panel CAL switch.
Prior to making use of the CAL switch, two transducer wires must be connected from the transducer to the
applicable channel’s CAL+ and CAL- terminals on the DBK65. The wiring section of the transducer’s
calibration data sheet will indicate which terminals (or wires) are to be connected.
To perform shunt calibration:
1.
Verify that each transducer to be calibrated has been properly connected to a DBK65
channel’s CAL+ and CAL- terminals.
2.
Ensure that the transducer has no initial load, i.e., that it is initially at “zero.”
3.
Adjust the data instruments zero-control to obtain a value of 0.0 volts.
In the case of 4 to 20 mA outputs, this value would be 4 mA.
4.
Slide the CAL switch on the DBK65 rear panel to the “CLOSED” position. Each channel’s
internal calibration switch will simultaneously close, activating the calibration shunts [if
present].
A step change in the channel output will occur.
5.
If the amount of the step change does not agree with the expected change as indicated by the
transducer’s calibration data sheet, adjust the transducer as needed. This is typically
accomplished with SPAN and/or GAIN control. Refer to the documentation for your specific
transducer.
6.
Return the “CAL” switch to the “OPEN” position. This removes the shunt calibration
resistance from each channel.
7.
Recheck the “zero.” Note that there may be some interaction if the GAIN or SPAN control
adjustments were large.
In regard to 4 to 20 mA circuits, several full cycles of adjusting the ZERO and SPAN controls
may be needed.