3160 - Oxygen Analyzer
We have a 3160 O2 analyzer at one location. They recently have substituted microfuel cell B2C.
Now restarting the analyzer they match the following problem:
During calibration Zero is OK
Span calibration gives a problem; They set as calibration value 8.8 ppm on FS 0-10 ppm
Display gives a warning "Cell too strong" press ACK, Re-try Span or press Esc to abort Span.
The cell strength is indicated to be 1.00 so it seems ok.
Note that this is the same message they have got before cell substitution and that's why they did decide to change the cell (the old cell strength was 0.8)
Could you please help us to understand the problem and suggest possible solution?
The 3160 has software in the unit that detects when the sensor output current is too much for a given concentration of span gas. The sensors have output current between 1.2nA per ppm up to 3nA per ppm. So for an example if the customer put in for sake of argument, 8ppm and the unit measured 40nA of sensor current, the unit would give this message of cell too strong.
There are several possibilities as to why they are getting this message now
a) the span gas tank is not accurately analyed somehow or is contaminated. So that it is given a O2 concentration that this more that it is suppossed to be.
Some things to consider:
what is the value of the O2 cylinder being used?
do they have another cylinder they can try?
2) maybe there is a leak of o2 somehow in the analyzer or the lines to the cylinder?
To see if this is the case, put the unit in the calibration mode and then vary the flow of gas through the analyzer. try this procedure http://www.teledyne-ai.com/tsfaq/faq_sensors.asp#q13
3) It would useful to see what the reading is of the span gas going into the unit after a cold start of the unit where the unit is returned to default values of all settings. If you could do a cold start by holding down the button the keypad on the far right (i think, but it might be the far left button also) and turn the power switch off and back on again, the unit should come up and say COLD START.
Then apply the span gas and without completing the calibration please report what the value of the span gas concentration is
4) If is possible the unit may have developed a electronic fault. Do you have a technician that can go to site to check the unit out with a Teledyne Cell simulator? If so, I can give a more detailed checking procedure on how to use the cell simlulator
Also it would be interesting to see what the unit reads with no sensor installed after a cold start. IT should read zero or close to zero.
5) please make sure that the exhaust of the sensor (sensor vent) is going to atmoshperic pressure
6) does this unit have internal cal zero valves? also, does it have scrubber? if so, please check to make sure the pressure on the valves is at least 70psi. please tell what the pressure is.
7) it may be that the customer did not wait long enough after sensor installation for the sensor to recover from the high level it gives after being exposed to air.
8) what type of regulator is being used on the span gas cylinder(is it a dual stage metal diagrpham cylinder) and was the regulator purged prior to use?
What is the gas concentration being applied at calibration and how long did they purge the unit before they attempted the calibration? what is the background gas the sensor is being used in?>>
In short the problems can be
a) bad electronics in unit
b) bad sensor - i would say this is unlikely but possible, if this is suspected, it might be good to check the date code on the sensor, or serial number, and try another one if there is one there
c) a leak in the tubing to the unit or internal to the unit
d) bad span gas, meaning the O2 content in the cylinder is higher than thought
e) not enough pressure on the cal valves
f) span gas regultaor not purged prior to use
g) customer not waiting for cell to stabilize after seeing span gas. It would be interesting to apply span gas to the unit and then see how stable the reading is over a few hours.
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