1B-14 / DP Transmitters 2808B
Figure 1B-15 - Closed Tank with Air Purge
The purge meter (pressure regulator) maintains a pressure on the dip tube that is
about 5% above the maximum pressure of a full tank. This prevents the liquid from
backing up the dip tube into the HI side of the Transmitter. For this application, the
liquid in the tank should not be allowed to exceed the maximum (100%) measurement
level or else it may backflow into the LO side of the Transmitter.
Head Error. A head error results whenever the transmitter is positioned above or
below the minimum (0%) measurement level of the tank. Head errors will add to or
sub-tract from the tank zero readings. These errors can be corrected during range
calibration to obtain the proper output readings. See Section 3 for calibration
information.
1B.6 SERVICE CHECKS
General troubleshooting hints are listed in Table 1B-B. Some of these checks will require a
digital multimeter (DMM). The DMM may be connected across the (+) and (V) terminals to
measure current directly without opening the current loop. See Section 4 - Service for
details.
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