2-9
EN
Deciding Which Trim
Procedure to Use
To decide which trim procedure to use, you must first determine whether the analog-
to-digital section or the digital-to-analog section of the transmitter electronics is in
need of calibration. To do so, refer to Figure 2-3 and perform the following procedure:
1. Connect a pressure source, a HART communicator, and an output device to
the transmitter.
2. Establish communication between the transmitter and the communicator.
3. Apply the desired 20mA point pressure (100 in H2O, for example).
4. Compare the applied pressure to the Process Variable (PV) line on the
Communicator Online Menu. If the PV reading on the communicator does not
match the applied pressure, and you are certain your test equipment is
accurate, perform a sensor trim.
5. Compare the Analog Output (AO) line on the communicator online menu to
the digital readout device. If the AO reading on the communicator does not
match the digital readout device, and you are certain your test equipment is
accurate, perform an output trim.
Sensor Trim
You can trim the sensor using either the full trim or the zero trim function. The trim
functions vary in complexity, and their use is application-dependent. Both alter the
transmitter’s interpretation of the input signal.
Microprocessor
Digital PV
Digital-to-Analog
Signal Conversion
Analog-to-
Digital Signal
Conversion
Transmitter Electronics Module
FIGURE 2-3. Transmitter Data Flow
with Calibration Options.
An
alog O
u
tput
Se
nsor Signal
HART Communications
100 inH
2
O
(Transmitter Ranged 0 to 100 inH
2
O)
PX2088S:PT-4763
Online
1 Device Setup
2 PV 100.00 inH2O
3 AO 20.00 mA
4 LRV 0.00 inH2O
5 URV 100.00 inH2O
Output Device
20.00 mA
Input Device
NOTES
1) Value on PV line should equal
the input pressure
2) Value on AO line should equal the
output device reading
1
2
3
4
If readings do not
match perform
sensor trim
If readings do
not match
perform
output trim
4690.bk : 4690.s2 Page 9 Tuesday, May 26, 1998 5:28 PM
