3-4 / Calibration 2808B
3.3 EXTERNAL CHECK PROCEDURE
The general check procedure determines the accuracy of the Transmitter at its calibrated
operating range. It uses the offset (A1) and the gain (A2) adjustment screws for minor
calibration corrections. Proceed as follows:
1. Provide a test setup as shown in Figure 3-1a or 3-1b depending on whether the unit has
been configured for current or voltage mode. Make sure that no electrical power is ap-
plied to the transmitter while making connections. The Multimeter must be set in
“Voltage” mode.
2. Set the DMM to a scale that will cover a 1-5Vdc range.
3. Apply 24Vdc power to the transmitter.
4. Set the pressure test source for a precise 0% range value. The DMM should display
1.00Vdc ± 4mV (4mA dc ± 0.016mA).
5. Similarly, adjust the pressure test source for 100% range value. The DMM should read
5.00Vdc ± 4mV (20mA dc ± 0.016mA).
6. If the readings of steps 4 to 6 are within tolerance, no calibration is required. Testing is
complete. However, if any readings were in error, proceed to step 7.
7. Set the test pressure source to 100%. If this reading is out of tolerance, correct it by
turning the A1 adjustment screw (clockwise rotation increases the reading).
8. Reset the test pressure source to 0%. If this reading is out of tolerance, correct it by
turning the A2 adjustment screw (clockwise rotation decreases the reading).
9. Recheck the 0%, and 100% readings. Repeat steps 7 and 8 as needed. This may need to
be done two or three times. If errors are still present at full-scale pressure, recheck the
switch settings. If the DIP Switch is in the correct configuration, proceed to step 10. If
errors are encountered at 0%, recheck the Rotary Switch settings. If the switch is in the
correct position, proceed to step 10.
10. If the above three readings cannot be brought into proper calibration, the transmitter
may require service or replacement. See Section 5, Service, for troubleshooting hints.
3.4 CALIBRATION ADJUSTMENTS
The range changing procedure uses the coarse span (SW1) and zero switches (S1:1-8), along
with the fine offset (A1), and gain (A2) adjustment screws. The locations of the switches are
shown in Figure 3-2. The equipment setup required to perform range changing is the same
as that described in topic 3.1. The coarse zero switches are contained in a single DIP switch
package, with the switches labeled from 1 to 8, with either a “1” or a “0” silk-screened on
the board. The coarse span switch is a 10 position rotary switch.
Coarse Span: The coarse span is set, by rotating the switch SW1, such that the desired
range of full scale is available. Span can be calculated using the formula below.
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