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Model 2120 Nitrogen in Argon Analyzer

What is the procedure to start up (including ZERO and SPAN calibration) the models 2120 and 3000TAEU? There are two cylinder gas, one is pure argon the other is 182ppm Ar in N2 at the plant site. What should we be careful about?
While starting up the model 2120 we encountered a problem.

First, pure argon(5N) in at 10:00AM, and purge. At 3:00PM, I cloud adjust 0.0ppm using ZERO pot on the front panel, things appeared OK.

Next, SPAN gas(182.9ppm Ar in N2) in at 3:30PM, and purge. At 7:00PM, it can NOT adjust to 182.9ppm using SPAN pot on front panel. The display kept "1" over range. When SPAN pot was set to 000, the display still kept "1" over range. I set 128mV at check pin of the back panel using PLATE ADJUST pot as detailed in a instruction manual. However, the display is still showed "1". The analog output was 33.43mA at this time. The inlet pressure was constant at 0.04MPa, the flow rate was 2 SCFH.

Why did it not adjust with the SPAN gas?
The regulator is purged overnight, however, when SPAN gas in, the display shows 182.9ppm for only the first 1 minute. After 1 minute the display become "1" over range and it can NOT adjust to 182.9ppm using SPAN pot on front panel. The display stays at "1" over range. When SPAN pot set to 000, the display still stays at "1" over range.

Next, the regulator is removed to ZERO gas cylinder. After then, zero gas in, the display become 0ppm after 10 minutes. So, I think the resulator is no problem.

Is there any reason about this problem? How do you adjust the 2120 to bring it back in range?
We have a 2120 that has not being operating since it was started up. It keeps on giving an over range alarm. The system has been purged with 99.999% argon for more than 48 hours. Flow through the unit is set at 2cfh and pressure is at 40 kPa. Sample system has been leak checked and no leaks were found. I applied the calibration steps as described in the manual as explained in chapter 4.2.3, set the millivolts as described, but still had no success. The mA reading is sitting at 28.3 mA.

Per chapter 4.4 of the manual it seems that the over range protection circuit is malfunctioning.

Also, with the cover of the instrument removed, the reading then comes down to 2ppm and responds to test gas. There is no glow in the PM tube.

Please advise as to any further steps that can be taken to rectify or pinpoint the fault.


What is the procedure to start up (including ZERO and SPAN calibration) the models 2120 and 3000TAEU? There are two cylinder gas, one is pure argon the other is 182ppm Ar in N2 at the plant site. What should we be careful about?

The key commissioning issue is to regulate the sample and cal gas inlet pressures to below 6 psig.

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While starting up the model 2120 we encountered a problem.

First, pure argon(5N) in at 10:00AM, and purge. At 3:00PM, I cloud adjust 0.0ppm using ZERO pot on the front panel, things appeared OK.

Next, SPAN gas(182.9ppm Ar in N2) in at 3:30PM, and purge. At 7:00PM, it can NOT adjust to 182.9ppm using SPAN pot on front panel. The display kept "1" over range. When SPAN pot was set to 000, the display still kept "1" over range. I set 128mV at check pin of the back panel using PLATE ADJUST pot as detailed in a instruction manual. However, the display is still showed "1". The analog output was 33.43mA at this time. The inlet pressure was constant at 0.04MPa, the flow rate was 2 SCFH.

Why did it not adjust with the SPAN gas?


Both zero and span regulators should be purged at least a few times. I think the manual states to purge each line for 8-12 hours, but I've purged for under three hours with no issue if everything else was done correctly. I typically purge span line, then zero, then power unit on zero gas.

If this does not solve the problem, they will need a voltmeter and potentiometer adjustment tool and will need to access the back of the unit to adjust a couple PCB pots. This may be required from time to time.

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The regulator is purged overnight, however, when SPAN gas in, the display shows 182.9ppm for only the first 1 minute. After 1 minute the display become "1" over range and it can NOT adjust to 182.9ppm using SPAN pot on front panel. The display stays at "1" over range. When SPAN pot set to 000, the display still stays at "1" over range.

Next, the regulator is removed to ZERO gas cylinder. After then, zero gas in, the display become 0ppm after 10 minutes. So, I think the resulator is no problem.

Is there any reason about this problem? How do you adjust the 2120 to bring it back in range?


The procedure is as follows:

1. Perform the calibration procedure per Section 4.2 of Teledyne’s Model 2120 Manual. It is important the Test Point voltage (from the terminal on the rear of the unit) be set to 126 mVDC as discussed in Section 4.2.3 #4.

2. If the analyzer reads correctly on zero gas but reads over-range and triggers the Overrange alarm, perform the Setting the Overrange procedure below.

Setting the Overrange

3. Apply zero gas.

4. On the rear of the unit, remove the plate covering the right portion by removing the screws. On the PCB on the left side, place a voltmeter on the red and black test points and adjust the GAIN potentiometer until red and black test points read 4.75 VDC.

5. Apply span gas.

6A. If the span gas concentration is that of the full-scale operating range (e.g. the analyzer range is 0-200ppm N2 in Argon and the gas is 200ppm N2 in Argon), set the THRESHOLD potentiometer until alarm LED is at the threshold of illumination. Both the light behind back panel and alarm light will be illuminated.

6B. If the span gas is less than the full-scale operating range (e.g. the analyzer range is 0-200ppm N2 in Argon and the gas is 180ppm N2 in Argon), set the THRESHOLD potentiometer until alarm LED is NOT illuminated If the concentration is fairly close to the range, adjust the potentiometer approximately half to one turn past the point of the LED not being illuminated.

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We have a 2120 that has not being operating since it was started up. It keeps on giving an over range alarm. The system has been purged with 99.999% argon for more than 48 hours. Flow through the unit is set at 2cfh and pressure is at 40 kPa. Sample system has been leak checked and no leaks were found. I applied the calibration steps as described in the manual as explained in chapter 4.2.3, set the millivolts as described, but still had no success. The mA reading is sitting at 28.3 mA.

Per chapter 4.4 of the manual it seems that the over range protection circuit is malfunctioning.

Also, with the cover of the instrument removed, the reading then comes down to 2ppm and responds to test gas. There is no glow in the PM tube.

Please advise as to any further steps that can be taken to rectify or pinpoint the fault.


Here is the procedure for setting the over range circuit. He can perform the whole procedure or just adjust the THRESHOLD pot until the over range goes out.

DO NOT TOUCH ANY OTHER POTS. Be sure your are adjusting the correct pot.

1.Run on zero gas. Open the back panel and set the photo diode GAIN pot to 4.5 to 5.0VDC using the test points on the board.

2.Run the over range gas and set the THRESHOLD pot until alarm just LED ILLUMINATES. Light behind back panel and alarm light on front should illuminate simultaneously.

3.Low flow will produce an over range light.

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