MKS 275420-1-GQ-T-00011, Instruction Manual

Page: 47 / 52

Series 275 Convectron Module with DeviceNet
Instruction Manual - 275502 47
7 Service and Maintenance
7.3 Troubleshooting - Symptoms and Possible Causes
Table 7-1 General Symptoms/Possible Causes.
SYMPTOM POSSIBLE CAUSE
Unit will not power-up Check for +11 Vdc to +26.5 Vdc power across pins 2 and 3 of the
DeviceNet connector. See Section 3.3 in the Installation chapter.
The Bridge analog output
voltage reads less than +0.22
Vdc or greater than +10 Vdc. Gauge tube failure. See Section 7.4 to check the gauge tube.
Bridge amplifier failure. Replace the Module.
Pressure readout cannot be
calibrated using the specified
calibration commands. The gauge tube is contaminated with material from the vacuum
chamber. Clean the gauge tube (see Section 7.5) or replace the gauge
tube.
If the gold plating on the sensor wire has been attacked by a gas such
as fluorine or mercury vapor, which has changed the emissivity or
resistance, cleaning the gauge tube will not solve the problem - the
gauge tube must be replaced.
The pressure readout from the
Mini-Convectron is vastly
different from that which is
observed by supporting
gauges on the vacuum system. The gas composition in the vacuum chamber may not be what the user
believes it to be. Determine the actual type of gas in the chamber, and
calibrate the Mini-Convectron Module accordingly. See Section
6.4 in the Calibration chapter.
Unexpected gas sources can also be caused by the process within the
chamber or outgassing of the product in the process chamber.
Pressure reading grossly in error. Controller out of calibration.
Unknown gas type.
Gauge not mounted horizontally. See Section 3.2. Sensor
damaged (e.g., by reactive gas) or dirty.
Extremes of temperature or mechanical vibration.
7.4 Convectron
Gauge Test Procedure
The small diameter sensor wire can be damaged by even small voltages. Do not perform electrical
continuity tests with instruments applying in excess of 1 volt when the gauge is at vacuum, or 5 volts
when at atmospheric pressure.
The Convectron Gauge should show the resistances listed in Figure 7-1. Pin numbers are embossed
on the gauge base. Measure the resistance across the pins with the gauge at atmospheric pressure,
using an ohmmeter that will not apply more than 10 mA.