Cooper Instruments & Systems DFI 7000 Digital Force Indicator - Manual (Page 5)

CF11 5 V-May 2003-008-0186-00
14.7 psi) and adjustment cannot be made using the ZERO adjustment only.
1. Remove the bezel and front panel with a small screwdriver.
2. Apply power to the DFI 7000. About 10 minutes warm-up is sufficient.
3. Adjust the COARSE ZERO potentiometer (see figure 1) to give an output voltage on terminals 10 and 11 of
zero. Then adjust the FINE ZERO to bring this value to exactly zero.
4.2 Span Adjustment
Span adjustment calibrates the gain of the amplifier section of the Signal Conditioner Board to provide the proper
voltage output for a given pressure or load. The shunt calibration feature allows the span to be properly set-up
without applying a known pressure or load to the transducer. This form of span adjustment will be described first,
followed by a method for calibration when the shunt calibration value has not been determined.
4.2.1 Span Adjustment With Shunt Calibration
A Transducer Calibration Record is normally shipped by all manufacturers of transducers with their products. The
full scale output and the shunt calibration output of unamplified transducers are reported on the Certificate of
Calibration in millivolts per volt (mv/v). Calculate as follows:
Shunt Cal Output in mv/v x Full-Scale Output = Output Voltage
Full-Scale Output in mv/v
EXAMPLES :
Using the calibration and full-scale output of the DFI 7000 (5V) provides:
1.4883 mv/v x 5V = 3.939 volts
1.8888 mv/v
After this calculation is made, proceed as follows:
1. Connect a meter to the output terminals (10, 11) on the rear connector.
2. Depress the SHUNT CALIBRATION button (See figure 1).
3. Adjust the COARSE SPAN control to give the approximate output voltage value calculated above.
4. Adjust the FINE SPAN control to give the exact output value calculated above.
After making these adjustments, a full scale pressure or load to the transducer will produce a 5-volt output from the
DFI 7000.
Note:
The Shunt Cal Output provided by the Transducer Calibration Record is determined using a particular value
of Shunt Cal resistor. That value is also specified on the Transducer Calibration Record. It is necessary that the
same value of resistor be installed to produce the same results. The normal value used by COOPER for
transducers is 59,000 ohms (59k). This value is installed in the pin jacks provided on the Signal Conditioner Board.
If the transducer being used has a different value specified for its shunt cal resistor, it will be necessary to install
this value in the jacks provided on the Signal Conditioner Board. A procedure for accomplishing this is given in the
section entitled “Changing the Shunt Calibration Resistor.
4.2.2 Span Adjustment, Without Shunt Calibration
If the transducer shunt calibration output is not specified or not known, span can still be adjusted, but a known
pressure or load must be applied to the transducer. The applied pressure should be as close to the full-scale value
as possible, so that tiny errors in slope are not amplified by the ratio of full-scale to calibration point values.
Calculate the expected output of the DFI 7000 as follows:
Known Pressure or Load X Full Scale Output = Output Voltage
Full Scale Pressure or Load
Once this calculation is made, proceed as follows:
1. Connect a meter to the output terminals (10, 11) on the rear connector.
2. Apply the known pressure or load to the transducer.
3. Adjust the COARSE SPAN control to give the approximate output voltage value calculated above.
4. Adjust the FINE SPAN control to give the exact output value calculated above.