Teledyne-API Model 200 NOx

TECHNICAL BULLETIN 102-3 January 2019 Issues: The Operations and Data Support Section’s Instrument Laboratory has noticed an increasing number of Teledyne-Advance Pollution Instrumentation (TAPI) model 200E Total Oxide of Nitrogen instruments being returned to the instrument laboratory for repair due to excessive drift and calibration issues. A common diagnosis with these instruments is the reaction cell (Rcell) sample flow and Rcell ozone flow inlets being clogged. This causes the flow rate displayed on front panel to be deceiving and may not reflect the actual sample and ozone flow readings of the instrument. To determine the actual flow rates of the instrument (sample and ozone flows), a direct measurement of the flows directly at the reaction cell block with certified or calibrated mass flow meter is recommended. Repair to these instruments has simply been to replace or rebuild the orifice holder assembly. Symptoms:

Common symptoms with the issue described above may be the following:

1. Span gas reading below the target or slow response.

2. High AZERO reading.

3. Gradual drifting of span calibration.

4. O-rings on ozone side of the Rcell fitting dissolves which results in the Rcell becoming contaminated.

5. Slope of the NOx and NO calibration out of range.

Solution:

Although the issue outlined in this technical bulletin has only been observed on TAPI model 200E instruments, this bulletin also applies to TAPI model T200/T200U instruments used in the ARB ambient air monitoring network. The solution to the issue outlined in this technical bulletin is to; 1) Replace the entire orifice holder assembly, (part number 04450) as shown in figure 2

or

2) Rebuild the assembly as shown in figure 3 with the proper parts (o-rings, sintered filter and clean critical orifice).

Cleaning the Rcell is highly recommended if you are having calibration issues. Refer to operational manual for details.

NOTE: Instrument laboratory staff recommend that the preventative maintenance

task to replace reaction cell o-rings and sintered filters be performed semi-annually instead of annually.

Tools needed:

1. 9/16” wrench

2. 7/16” wrench

3. Portable 4 in 1 mass flow meter

4. small flat screw driver for PMT and gain adjustment

5. 1/8” fitting/tube adapter

NOTE: Perform a leak check and resolve any leak issues before and after this procedure.

Procedure:

Step 1 (Orifice holder replacement/rebuild)

1. Remove the unit cover, while the unit is still running.

2. Loosen and remove the sample flow inlet fitting with 1/8” tubing as shown in figure 2 below with a 7/16” wrench.

3. Connect a mass flow meter to measure sample side and ozone side respectively

(sample side: 500sccm ± 50, ozone side: 80 sccm ± 15) 4. If the mass flow meter reading is below or above flow rates stated above, turn

off power to the unit and vacuum pump and replace the orifice holder or rebuild the assembly with the correct two o-rings, 1 sintered filter, 1 spring and 1 critical orifice (Note that the critical orifice maybe reused after cleaning with deionized water).

5. After rebuilding or replacing the assembly, reconnect all the tubbing, vacuum

pump, and power up the unit, confirm that the sample and ozone flow readings are within the specification or threshold.

6. Perform a leak check after operating the instruments for approximately 30

minutes. 7. If the unit passes a leak check and the sample and ozone flow are within

specifications, proceed to the next step.

Step 2 (Pre-amp board adjustment)

1. Set your HVPS between 740-760V and should not be more than 800V.

2. Adjust the instruments Normal PMT reading to the corresponding span concentration. Note: Normal PMT reading should be twice greater than the targeted concentration, for example, for a 400PPB target, the Normal PMT reading should be around 800V (i.e. 400 X 2).

3. Run zero air/span gas and multi point check respectively and compare the result

with your reference values. Normal PMT is adjusted with the gain adjustment, R29 on the Pre amplifier board as shown in figure 4 below (Pre amplifier board layout).

NOTE: Over adjustment on the gain could lead to noisy reading and high AZERO reading. It is recommended to adjust the gain 24 hours after replacing the orifice assembly or cleaning reaction cell for optimal result.

Sample flow, 1/8” tubing

Ozone flow, 1/8”tubing

Figure 1: Reaction cell block and the sample and ozone tubing

Orifice holder 10 mil and 4mil

Removing orifice holder

Figure 2: Removing the critical orifice holder assemble/orifice holder

Figure 3: Orifice holder assembly

Figure 4: Pre amplifier board assembly

Contact: Frank Uwazie Instrument Tech, Air Quality Phone #: 916-324-7333 Email: fuwazie@arb.ca.gov