Measurement Computing DBK Part 2 - Manual (Page 46)

DBK43A & DBK43B, pg. 26 899892 DBK Option Cards and Modules
There are four trimpots to set up each channel circuit. The trimpots are labeled to represent the following
adjustments:
• EXC - for adjusting the excitation voltage to the transducer
• GAIN - for setting the gain of the input amplifier
• OFFSET - for adjusting the circuit offset for quiescent loads or bridge imbalance
• SCALE - for setting the gain of the scaling amplifier
Signal-FlowRelationship of Software Controlled Multiplexers and On-Board Reference Voltages
This calibration procedure can only be executed while LogBook is attached to a PC that
is running LogView.
To adjust trimpots, use one of the following calibration methods, as appropriate.
Calibration Methods
Several different calibration techniques are supported by strain gage signal conditioning modules.
Calibration methods include; Nameplate, 2-Point, Shunt, and Manual. From the following discussion,
select the calibration method that is best for your application.
Nameplate – Used to setup the channel using the transducer’s published specs.
Nameplate calibration is typically used with packaged load cells with millivolt-per-volt (mV/V) transfer
functions. Using the mV/V spec of the load cell or a strain gage’s Gage Factor (GF), the necessary system
gain can be calculated and applied to a channel.
2-Point – Used to setup the channel using 2 known loads, one of which might be “no load.”
The 2-Point calibration method requires the operator to apply two known loads to the load cell or strain
gage, one at a time, while the data acquisition system takes measurements. Typically, the first point is with
no load applied and the second point is close to the maximum load capacity of the gage. While measuring
the first point the offset is nulled, and while measuring the second point the gain is adjusted to span the
majority of the input range of the A/D. No gain calculations are required to perform this calibration
method.