Measurement Computing DBK Part 2 - Manual (Page 45)

DBK Option Cards and Module 899892 DBK43A & DBK43B, pg. 25
Calibrating DBK16, DBK43A, or DBK43B for LogBook Applications
Overview …… 25
Calibration Methods …… 26
Procedures Common to All Calibration
Steps (Required) ……27
Nameplate Calibration and
Manual Calibration ……30
Channel Calibration Procedure ……33
2-Point Calibration ……36
Shunt Calibration ……38
Creating a Units Conversion Transfer Function ……40
Periodic Calibration Without Trimpots ……41
Overview
Calibrating a strain gage channel includes:
One-time adjusting of the bridge excitation.
One-time tuning of the electronic gains and offset via trimpots to maximize performance and
dynamic range.
Applying a transfer function to the voltage output to convert it to engineering units, e.g., pounds,
kilograms.
Executing a software scale and offset adjustment periodically to maintain accuracy.
Example of a Unit Conversion from Voltage to Pounds
The trimpots provide course tuning so large quiescent offsets can be nulled and the bridge signal can be
amplified to match the A/D input range. Once these adjustments are made, the operator can periodically
fine-tune the calibration via software using LogView’s 2-Point calibration feature. LogView’s scale and
offset features provide a simple means to apply a transfer function that converts the voltage to user units,
for example, pounds, as in the above block diagram.
Bridge circuit transducers are used for many different applications, and the strain gage signal conditioning
modules are flexible enough to support most of them. Each channel circuit has an excitation regulator, a
high gain (x100 to x1250) input amplifier with offset adjustment, a low-pass filter, a scaling (x1 to x10)
amplifier, and a calibration multiplexer.
By using software-controlled multiplexers, on-board reference voltages can be read by the data acquisition
system so that precise gains and offsets can be set. LogView provides a means of easily controlling the
calibration multiplexers so that the reference voltages can be displayed while the trimpots are being
adjusted.