If we used pure gas (< 10 ppb O2) from another purifier or sample, how long might it take to clean-up electrolyte that is the cause of a high background level and thus prevents zero cal?
If we choose to use external zero gas, does this gas flow through the internal zero scrubber during zero calibration or does it bypass the scrubber?
Regarding the 3160 - Just before zeroing the value is 0.002 ppm. When zeroing, the value goes to -0.17 ppm, and stays there, allthough nothing changes in gas flow. When the zeroing is carried out, the system works like it should (gives 0 on zero-gas and correct values for span-gas). Yet, in the past this signal-dip did not occur. What could be wrong?
1. With regards to the 3060E O2 scrubber, the scrubber can scrub 200 cc of pure 100% O2 (per vendor O2 scrubber life information). Using this info, calculations were made. If 1 ppm of O2 is being scrubbed at a rate of 150 ccm, this translates to 2.5 yrs of life. Considering that doing the connection of the scrubber to the analyzer, the scrubber is exposed to air (21% O2) for a brief time - the life of the scrubber will be decreased to approximately 1.5 to 1.75 yrs (at 1ppm at 150 ccm). If the scrubber is exposed to air even longer, the life will decreased substantially.
2. So if 400 ppb is being scrubbed, then the scrubber life increase by factor (1ppm/400ppb = 1000ppb/400ppb = 2.5 times). So, 1.5 to 1.75 years times the 2.5 factor = 3.75 to 4.37 years at 400 ppm level at 150 ccm flow.
FYI, we have scrubber in the back of the lab which supply many O2 instruments (as many as 15 units - 316, 3000 type) and the scrubber has lasted 2-1/2 years. Also, the manual says under scrubber maintenance section that the scrubber should last for several years under normal use.
The electrolyte must be replaced when the background signal is usually high and analyzer is unable to be adjusted to zero. A high level could be the result of dissolved O2 in the solution which occurs when the sensor is exposed to high O2 concentrations for long periods of time.
This also occurs when the analyzer has been in use for a long period of time. Also to keep in mind is the Cadmium anode usage - when the O2 is reduced at the cathode, cadmium is oxidized producing Cadmium +2 ions in the electrolyte. Replacing the electrolyte will reduce the high level of ions which build up in the solution when the analyzer is in use for a long period of time. For best results, it is recommended to change the electrolyte once a year to 1-1/2 yr. Replacement instructions are in the manual.
If the replacement electrolyte is properly purged with zero gas (at least 1 hour) prior to removing the old electrolyte, the replacement process should not take more than 10-15 mins. Down-time to ppb range can range any where from 10-24 hours. Replacement instructions are in the manual.
The analyzer can be zeroed with zero gas generated by the built in zero gas scrubber or by using external zero gas. In order to choose external zero gas press SETUP from the analyzer mode. Instructions are in the manual in the SETUP: Zero/Span Gas Source section.. Keep in mind that the zero gas from the scrubber also supplies the zero gas for sparging the electrolyte inside the sensor (to remove the dissolved O2).
Not really. In Zero Calibration Mode, the unit display the value of the background current of the sensor as expressed as O2 units. (i.e. 75ppb of background current, 100 ppb of background current, etc).
This unit has an onboard O2 scrubber. When you go into zero mode, you should force the sample gas through the O2 scrubber which will remove O2 from the sample.
If you get a lower reading in zero mode than you do in the analyze mode of the unit, it is usually because the unit was zeroed previously at a higher level of actual O2 in the sensor. This is not necessarily abnormal.
If the unit is working properly apart from this, there may not be anything wrong with the unit at all.
You may want to check the unit out with a microfuel cell simulator, and also consider changing the scrubbe. When the scrubber gets old, the unit will not function properly.
One of our 3060E oxygen analyzers reveals a thermal problem/effect. The analyzer is supported with high purity nitrogen with a typical oxygen-level < 0.1 ppm. At slightly elevated temperatures, as is normal for a rack (about 30C), the analyzer reading drops down from typically 20-30 ppb to -12.5 ppb. The effect is reversible when cooled down to normal temperature (about 20-22C) -- the analyzer works well.
The analyzer temperature setting is 28 deg C. This is the temperature at which the oven is to be controlled. The thermistor that is installed on the top of the sensor is used to compensate for minor temperature changes.
Have you checked to see if the reading will return to normal after a some time is allowed for the temperature to reach equilibrium? or will the reading remains negative at the higher temp.
It is possible that the thermistor is not functioning properly at the temperatures above 28 degs C. The thermistor is about 16Kohms at 25 degrees C. The resistance should increase as temp. decreases, and decrease as the temp increase.
You might also check the temperature sensor inside the analyzer. It can be accessed from the rear of the instrument. Both the top and bottom displays on this module should be 28. If they are not matching, there are up/down switches that can be used to make adjustments.
Please note this picture. There are three jumpers on the analog output board which is contained inside the control module of the unit.
The middle jumper tells the unit's microprocessor if the unit has one cell or two. The two cell position is up (as shown), while one cell is down.
The right most jumper block, when configured down, tells the microprocessor that the unit has no scrubber, while when up, the unit has as scrubber. In the picture, the board is set up for no scrubber.
Note: Before using the Type A electrolyte in the 3060E cell, it is recommended that the electrolyte be properly pre-purged with zero gas (usually scrubbed N2 gas) at least 1 hour prior to removing the old electrolyte from the cell. The reason for pre-purging is to decrease the down time to achieve a faster zero offset reading. Electrolyte replacement instructions are in pages 3-4 to 3-8 of the 3060E manual. The replacement process should not take more than 10-15 mins.
Important: You should never use electrolyte A64239 inside the cell - A64239 is used only for the calibrator. Electrolyte A51934 is 10% KOH and should only be used inside the cell.