Troubleshooting Unexpected Readings - Teledyne 8800A Operating Instructions Manual

8800 Series Trace Moisture Analyzer Instruction 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
Reading is not Condensation in sample system.
changing
1. Water vapor in the system.
Slow Response 2. Flow rate too low.
3. Sample pipe too large and/or too long.
4. Unsuitable sample pipe.
5. Leaks.
6. Hygroscopic materials in sample system
Dry Reading SpanCheck™, wrongly set, or faulty Sensor.
Leak in system or use of unsuitable pipe.
Wet Reading
Comparison of readings with manual cooled-
mirror instrument.
Display Shows Prolonged exposure to wet gas.
SAT
1. Instrument Failure
Display Shows 2.Short circuit on sensor cable or connections.
SHR
3.Short circuited sensor.
1. Instrument failure.
Display Shows
OPN 2. Open circuit on cable.
.
3. Open circuit on sensor.
For non-sensor related problems (e.g. no reading on instrument) refer to section 3.6
Possible Cause Diagnostic/Remedy
Condensation will occur if the temperature of the sample system, at any point is below
(colder) the dewpoint temperature of the sample gas. Once having formed, the sample
reaching the sensor will have a dewpoint equal to the temperature of the condensation,
regardless of the dewpoint of the source gas.
It is usually more satisfactory to bleed a sample gas at atmospheric pressure through
the sensor sampling chamber, and to use 1/8" (3mm) o.d. sample pipe.
See below re sample pipe material, also see section 2.3
Verify SpanCheck™, or return sensor for full calibration to your representative.
Cure the leak, or replace unsuitable pipe with copper or stainless steel. Flexible con-
nections should be made with PTFE pipe. NEVER use rubber or plastic pipe.
This type of indicator reads about 10ºC dry at about -50ºC dewpoint due to tempera-
ture gradients within the device. The error increases at drier levels.
Dry down the sensor, install sensor in either a known dry gas stream i.e. instrument
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
Disconnect cable from input terminals, if the instrument still reads
is with the instrument. However, if the instrument reads
to the input terminals and check possible causes 2 or 3.
Disconnect cable from sensor and if meter still reads
cable or connections or replace cable; otherwise check the sensor.
Disconnect cable from sensor and note that the meter reading returns to
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.
Short the SIG and SHIELD contacts of the sensor input terminal, if the instrument
SHR
reads the problem is in the cable or sensor, otherwise return the instrument for
service.
Disconnect cable from sensor and short center pin of plug to the outer shell. If the dis-
OPN
play still shows , repair cable.
Check sensor connection or replace sensor.
8
SHR
the problem
OPN
then recconect the cable
SHR
, cure the short circuit in the
OPN
. Use a