Teledyne OT-3 - Manual (Page 40)

Maintenance OT-3
Teledyne Analytical Instruments 32
Figure 5-1: AC Fuse Replacement
DC Units
On DC units, the fuse is located in a fuse holder on the rear panel.
See Figure 1-3. Unscrew the cap on the fuse holder and remove the
blown fuse. Replace the fuse with a 1/2 A micro fuse P/N F91.
5.2 Sensor Installation or Replacement
5.2.1 When to Replace a Sensor
On trace analyzers the Micro-fuel Cell will typically fail due to
excessive zero offset caused by loss of water. Large zero offsets will
result in inaccurate SPAN settings. To test for this condition, purge the
sensor and sample system with ZERO gas (typically nitrogen with less
than 1 ppm O
2
).
To do this, you should connect a pressure regulated zero gas source
to the instrument at the span gas port. This can be done by either
shutting off the span gas and replacing it with the zero gas supply or by
teeing into the span gas line using a selector valve which can then feed
either span or zero gas to the instrument.
It may take several hours for the sample system and cell to return to
a stable low level of O
2
if it has been exposed to higher levels of O
2
. If
the instrument will not come down to an acceptably low reading on zero
gas, then a depleted cell or a sample system leak should be suspected.
Typically offsets of 1.0 ppm or less are acceptable. A cell failure
may also be indicated by an inability to SPAN, or slow response to
changes in O
2
concentration at levels below 100 ppm.