Teledyne Sensor Installation or Replacement, Maintenance OT-3, When to Replace a Sensor

Maintenance OT-3

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.

5.2Sensor 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 O2).

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 O2 if it has been exposed to higher levels of O2. 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 O2 concentration at levels below 100 ppm.

Teledyne Analytical Instruments 32