Troubleshooting; Diagnostic Features; Stroke Port; Remote Pressure Reading (Rpr) - Emerson Fisher 846 Instruction Manual

Instruction Manual
Form 5739
February 2002
Section 5

Troubleshooting5-5-

The modular design and unitized subassemblies of
the Type 846 and Model 3311 allow for quick and
easy troubleshooting and repair. This section
presents information on the diagnostic features and
procedures for troubleshooting both models in
service or in the shop.

Diagnostic Features

If a control loop does not perform properly and the
cause of malfunction has not been determined, two
features of the transducer can be used to determine
if the transducer is at fault: the stroke port and
Remote Pressure Reading.

Stroke Port

The stroke port provides a way to quickly increase
the transducer output, giving a rough measure of the
unit's functionality. A hole in the module cover vents
the constant bleed from the pilot stage. When the
hole is covered, pressure at the pilot stage receiver
nozzle increases, which in turn increases the output.
Output pressure will increase to within 2 psi of
supply pressure for either direct or reverse action. If
output pressure does not increase to this level, it
may indicate that supply air is not reaching the pilot
stage or that a pilot stage nozzle is plugged.
If the stroke port diagnostic feature is
not desired, the transducer is
available with an optional cover that
contains multiple stroke ports, as
shown in figure 2-1. This prevents
increasing the output by covering the
stroke port.

Remote Pressure Reading (RPR)

Remote Pressure Reading (RPR) is an optional
diagnostic feature that enables the user to determine
the output pressure from any location along the
signal wire path. For loop troubleshooting, this
allows the user to confirm the functionality of the
transducer from a remote location.
A frequency signal directly proportional to the output
pressure is superimposed on the input signal loop.
The frequency range of the RPR function is 5,000 to
8,000 Hz.
Note
Troubleshooting
A jumper on the circuit board activates the Remote
Pressure Reading function. Section 6 Maintenance
provides instruction on positioning the jumper. The
jumper, shown in figure 6-5, has two positions: N for
ON, or D for OFF. The RPR jumper is in the N (ON)
position when the unit ships from the factory, unless
otherwise specificed.
R
Using the HART Communicator to Read the RPR
Signal
The RPR frequency signal can be measured at any
location along the two input wires using a HART
Communicator. The HART Communicator displays
both the output frequency in Hertz and the
transducer output pressure in psi. Figure 5-1 shows
the wiring connections.
The transducer is not a microprocessor-based
transmitter and therefore does not identify itself to
the HART Communicator. For this reason, the
HART Communicator displays a screen telling the
user it cannot verify that the transducer is on the
loop.
Neither the HART Communicator nor the Remote
Pressure Reading function are intended to be used
for calibration. They are intended as a diagnostic
feature. The accuracy of the Remote Pressure
Reading function when used in conjunction with the
HART Communicator is typically ±3% of span and
guaranteed to be a maximum of ±6% of span.
When the output of a smart
transmitter is used as the input to the
transducer, the HART Communicator
will not recognize the frequency
signal of the transducer. Enabling the
RPR feature on the transducer can
also cause errors when trying to
communicate with a smart transmitter
using a HART Communicator. For
these reasons, you should disable the
RPR feature on the transducer when
using this type of loop.
Use the ON/OFF key (figure 5-2) to turn the HART
Communicator on and off. When the communicator
is turned on, it searches for a HART compatible
device on the 4 to 20 mA loop. If a device is not
found, then the communicator displays the
message, ''No Device Found. Press OK.'' Press OK
(F4) to display the Main menu (figure 5-3).
If a HART-compatible device is found, the
communicator displays the Online menu.
Note
5–1