Omega Engineering OMB-DBK-34A, User Manual

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DBK Option Cards and Module
879895
DBK16, pg. 13
Launch DaqView and set it up for the DBK16 at the correct Daq device input channel determined by the
setting of JP1 and S1. On return to the DaqView main spreadsheet screen, notice the
type column in the
spreadsheet. All the DBK16 channels should say
bridge
. Changing the type will allow us to set the offset
and gains in the DBK16. When setting up the DBK16 gains, enable only the channel you are setting up.
Turn all the others off in DaqView. Also, set DC coupling and disable the on-board filter during the gain
and offset settings.
First, we want to remove all the offset adjustment from the circuit. Set the type to Offset Gain . Enable the
input reading column from the Acquire menu or the tool bar. While reading the spreadsheet, set the
trimpot labeled OFFSET to read a value of 0.00. Disable the input reading column.
Next, set the type to Input Gain. This allows us to set the input amplifier gain. The DBK16 has a 5 mV
signal on the input, so the reading that we want to set the trimpot labeled GAIN to is (.005)(Input Gain).
Enable the input reading column and set the Input Gain. Disable the input reading column.
Typical Input Gain settings:
Gain DaqView Reading Gain DaqView Reading
100 0.5 volts 200 1.0 volts
300 1.5 volts 400 2.0 volts
500 2.5 volts 600 3.0 volts
700 3.5 volts 750 3.75 volts
800 4.0 volts 900 4.5 volts
1000 5.0 volts 1200 6 volts *
* requires DaqBook/DaqBoard to be in unipolar mode.
Next set the type to Scaling Gain . This allows us to set the scaling amplifier gain. When setting the
scaling gain, the input gain is also present and must be considered when making the adjustment. The
scaling gain reading you want to read is (.005)(input gain)(scaling gain). Enable the input reading column,
and set the Scaling Gain. Disable the input reading column.
For an input gain of 200 , typical scaling gains are:
Scaling Gain DaqView reading
2 2.0 volts
4 4.0 volts
6 6.0 volts*
8 8.0 volts*
10 10.0 volts*
* requires DaqBook/DaqBoard to be in unipolar mode.
Now all the gains are set correctly, and we have to adjust the offset for any bridge circuit imbalance or
quiescent loads. Enable the on-board filter. Set the type to
Bridge. Make sure the quiescent load is
applied. Enable the input reading column and adjust the trimpot labeled OFFSET for a reading of 0.00. If
you can not adjust it to 0.00, try dropping your input gain and compensate for the drop by raising your
scaling gain. If it still does not adjust to 0.00, swap the +BRG and -BRG wires to reverse the polarity of
the signal. The offset adjustment is unipolar and only affects the input gain.
After the final offset is
made, the gain readings will be incorrect (if you want to go back and check them) unless the circuit
offset is removed.
(Step 7 in typical setup procedure.)
Using the DBK16 with 3-Wire Strain Gages
Each single-element 3-wire strain gage has 1 wire connected to one side of the gage element and 2 wires
connected to the other. Follow these steps for using the DBK16 with the 3-wire single-element strain
gages.
1. Install bridge completion resistors R12 and R13 (R24 and R25 for lower channel).
2. Attach the 1-wire side of the gage element to the -EXC and -SEN terminals.
3. Attach one wire on the 2-wire side of the gage to +BRG terminal.
4. Attach one more bridge completion resistor to the end of the other wire on the 2-wire side of the
gage element.
5. Attach the other side of the 3rd bridge completion resistor to the +EXC terminal.