Instruction manual
MODEL Xmt-P SECTION 10.0
TROUBLESHOOTING
or terminals.
4. Connect a jumper wire between the RTD RETURN and RTD SENSE terminals (see wiring diagrams in Section 3.0).
5. If noise and/or offsets disappear, the interference was coming into the analyzer through one of the sensor wires.
The system can be operated permanently with the simplified wiring.
D. Check for extra ground connections or induced noise.
1. If the sensor cable is run inside conduit, there may be a short between the cable and the conduit. Re-run the cable
outside the conduit. If symptoms disappear, there is a short between the cable and the conduit. Likely a shield is
exposed and touching the conduit. Repair the cable and reinstall it in the conduit.
2. To avoid induced noise in the sensor cable, run it as far away as possible from power cables, relays, and electric
motors. Keep sensor wiring out of crowded panels and cable trays.
3. If ground loops persist, consult the factory. A visit from a technician may be required to solve the problem.
10.5.7 Process pH readings are noisy.
A. Is the sensor dirty or fouled? Suspended solids in the sample can coat the reference junction and interfere with the
electrical connection between the sensor and the process liquid. The result is often a noisy reading.
B. Is the sensor properly wired to the analyzer? See Section 3.0.
C. Is a ground loop present?
10.7 SIMULATING INPUTS - pH
10.7.1 General
This section describes how to simulate a pH input into the transmitter. To simu-
late a pH measurement, connect a standard millivolt source to the transmitter. If
the transmitter is working properly, it will accurately measure the input voltage
and convert it to pH. Although the general procedure is the same, the wiring
details depend on whether the preamplifier is in the sensor, a junction box, or the
transmitter.
10.7.2 Simulating pH input when the preamplifier is in the analyzer.
1. Turn off automatic temperature correction (Section 7.5). Set the manual tem-
perature to 25°C.
2. Disconnect the sensor and connect a jumper wire between the pH IN and the
REFERENCE IN terminals.
3. From the Diagnostics menu scroll down until the "pH input" line is showing. The pH input is the raw voltage signal in
mV. The measured voltage should be 0 mV and the pH should be 7.00. Because calibration data stored in the ana-
lyzer may be offsetting the input voltage, the displayed pH may not be exactly 7.00.
4. If a standard millivolt source is available, disconnect the jumper wire between the
pH IN and the REFERENCE IN terminals and connect the voltage source as shown
if Figure 10-1.
5. Calibrate the controller. Use 0.0 mV for Buffer 1 (pH 7.00) and -177.4 mV for Buffer
2 (pH 10.00). If the analyzer is working properly, it should accept the calibration. The
slope should be 59.16 mV/pH and the offset should be zero.
6. To check linearity, set the voltage source to the values shown in the table and veri-
fy that the pH and millivolt readings match the values in the table.
10.6 TROUBLESHOOTING NOT RELATED TO MEASUREMENT PROBLEMS
FIGURE 10-1. Simulate pH
Voltage (mV) pH (at 25°C)
295.8 2.00
177.5 4.00
59.2 6.00
-59.2 8.00
-177.5 10.00
-295.8 12.00
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