Epson XDT manual Troubleshooting unexpected readings, Symptom, Possible Cause, Diagnostic/Remedy

XDT User’s Manual

2.5 Troubleshooting unexpected readings

If erroneous readings are suspected on a newly acquired instrument, compare the serial number engraved on the sensor sintered filter, to the label on the instrument. The two should be the same; if they are not, the instrument may not be calibrated with the installed sensor. To troubleshoot other problems, identify the unexpected reading category in the following table, and consider the possible causes and appropriate diagnostic action and remedy.

Symptom		Possible Cause	Diagnostic/Remedy
			Condensation will occur if the temperature of the sample system, at any point is below
Reading is not	Condensation in sample system.		(colder) the dewpoint temperature of the sample gas. Once having formed, the sample
changing			reaching the sensor will have a dewpoint equal to the temperature of the condensation,
			regardless of the dewpoint of the source gas.
	1.	Water vapor in the system.	It is usually more satisfactory to bleed a sample gas at atmospheric pressure through
Slow Response	2. Flow rate too low.		the sensor sampling chamber, and to use 1/8” (3mm) o.d. sample pipe.
	3.	Sample pipe too large and/or too long.
	4.	Unsuitable sample pipe.
	5.	Leaks.
	6.	Hygroscopic materials in sample system	See below re sample pipe material, also see section 2.3
Dry Reading	SpanCheck™, wrongly set, or faulty Sensor.		Verify SpanCheck™, or return sensor for full calibration to your represent ative.
	Leak in system or use of unsuitable pipe.		Cure the leak, or replace unsuitable pipe with copper or stainless steel. Flexible con-
Wet Reading			nections should be made with PTFE pipe. NEVER use rubber or plastic pipe.
	Comparison of readings with manual cooled-		This type of indicator reads about 10ºC dry at about -50ºC dewpoint due to tempera-
	mirror instrument.		ture gradients within the device. The error increases at drier levels.
Display Shows	Prolonged exposure to wet gas.		Dry down the sensor, install sensor in either a known dry gas stream i.e. instrument
SAT			quality air or dry nitrogen, or place sensor in a dry can or bottle of desiccant and seal
			the container from outside air (the shipping container is designed for this purpose)
			also see section 3.4.4.3.1
	1.	Instrument Failure	Disconnect cable from input terminals, if the instrument still reads SHR the problem
			is with the instrument. However, if the instrument reads OPN then reconnect the cable
			to the input terminals and check possible causes 2 or 3.
Display Shows	2.Short circuit on sensor cable or connections.		Disconnect cable from sensor and if meter still reads SHR, cure the short circuit in the
SHR			cable or connections or replace cable; otherwise check the sensor.
	3.Short circuited sensor.		Disconnect cable from sensor and note that the meter reading returns to OPN. Use a
			new sensor, or apply approximately 20V DC to the sensor MOMENTARILY with the
			sensor in a known dry condition. Polarity is not important, but the contact MUST be
			very brief or the sensor may be damaged. Consult with your representative for a cir-
			cuit diagram.
			Short the SIG and SHIELD contacts of the sensor input terminal, if the instrument
Display Shows	1.	Instrument failure.	reads SHR the problem is in the cable or sensor, otherwise return the instrument for
			service.
OPN.
	2.	Open circuit on cable.	Disconnect cable from sensor and short center pin of plug to the outer shell. If the dis-
			play still shows OPN, repair cable.
	3.	Open circuit on sensor.	Check sensor connection or replace sensor.

For non-sensor related problems (e.g. no reading on instrument) refer to section 3.6

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