User manual

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.
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:
Nameplate, 2-Point, Shunt, or Manual.
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 –uses 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 – uses 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.
DBK16, pg. 16 879895 DBK Option Cards and Modules