Omega Engineering OMB-DBK-34A, User Manual

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Calibrating DBK16 for Daq Devices
Reference Note :
This section covers calibrating a DBK16 that is being used in a Daq device application.
LogBook users: refer to Calibrating DBK16 and DBK43A for LogBook, which begins on page 15.
Bridge circuit transducers are used for many different applications, and the DBK16 is flexible enough to
support most of them. Each DBK16 channel circuit has an excitation regulator, a high gain (100-1250)
input amplifier with offset adjustment, a low-pass filter, a scaling (1-10) amplifier, and a calibration
multiplexer.
There are 4 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
Proper setup includes the use of software commands that control the calibration multiplexer in each circuit.
The calibration multiplexer is used to switch the bridge circuit out and apply reference voltages to the input
for use in the DBK16 setup. The calibration multiplexer also allows the Daq device to record the
individual adjustments. The next table shows the setup commands, their binary codes, and a description of
their function. These commands are accessible through DaqView and the Daq device driver as gain
settings and through most third party software support as well as GageCal.
Setup Command Code Description
Dbk16ReadBridge 00 Reads bridge circuit with all gains and offsets included (normal operation)
Dbk16SetOffset 01 Applies a grounded input and allows the user to read the circuit offset voltage
multiplied by the input amplifier and the low-pass filter gain.
Dbk16SetScalingGain 10 Applies 5 mV to the input and allows the user to read the voltage out of the
circuit through the input gain amplifier, the low-pass filter* and the scaling
gain amplifier.
Dbk16SetInputGain 11 Applies 5 mV to the input and allows the user to read the voltage out of the
circuit through the input gain amplifier and low-pass filter only.
The following equations represent the voltage recorded by the Daq device when the calibration mux is
set in 1 of 4 possible settings.
Code Equation
00 Vout = (Scaling Gain)(Filter Gain*)[(InputGain)(bridge circuit voltage) - offset voltage]
01 Vout = (Filter Gain*)(Input Gain)(-offset voltage)
10 Vout = Filter Gain*(Scaling Gain[(Input Gain)(5 mV) - offset voltage])
11 Vout = (Filter Gain*)(Input Gain)(5 mV) - offset voltage
Asterisk (*) implies the filter is enabled.
A typical setup procedure is as follows:
1. Disable the low-pass filters (JP4 and/or JP5) and set DC coupling (install JP2 and/or JP3) for all the
channels that are being setup. If you plan on using the filter during your acquisition, take note of the
gain in the filter stage (default ×2, or ×1 with resistor removed) and allow for it in your setup.
2. Determine what the excitation for the transducer will be from the transducer specifications and the
current limitations of the DBK16 excitation regulator.
3. Determine what the maximum voltage will be from the transducer at maximum load or strain, and
calculate what the DBK16 channel total gain should be based on a full-scale Daq device
(-5 V to +5 V for DaqBook and DaqBoard [ISA type] in bipolar mode; 0 to +10 V for
DaqBook [/100 & /200], DaqBoard [ISA type] and DaqBoard/2000 in unipolar mode; -10 to +10 V
for DaqBoard/2000 in bipolar mode and Daq PC-Card). (See examples on page 12.)
DBK Option Cards and Module
879895
DBK16, pg. 9