Calibration – Dasibi Ozone Monitor

Using the 1008-PC Model

When to Calibrate If an ozone monitor is out in the

field, must be done every (3) months per CFR 50 regulations.

Must be done after replacing the ozone scrubber assembly, solenoid valve, pump, or UV lamp.

NOTE: Make sure to complete the Performance checks before proceeding.

Connect the scrubber to a particulate matter filter and then to inlet.

Connect one ozone output manifold to inlet of 1008-PC.

Connect second output to another monitor to be calibrated.

Make sure each connection is firmly attached to each port for air flow.

Setting Up the Calibration

Calibration Procedure with 1008-PC 1. After connections are set properly, set the mode to ‘Operate’ and turn

on the 1008-PC and the other monitor to be calibrated. Set the switch next to the thumbwheel to ‘Auto.’

2. The instrument will be tested at concentrations of 400, 300, 200, 90,

50, and 0 ppb. Start with 400 ppb and decrease.

Make sure to allow each instrument being calibrated to run for at least an hour so the lamp and other elements inside reach operational temperatures. The lamp is the main element that needs to be warm, so the pumps can be off.

For 0 ppb, make sure to turn the ozone generator switch to ‘Off’ and switch from ‘Auto’ to ‘Manual’ mode, or else sporadic ozone readings may result.

Calibration Procedure 3. Note the response time of each instrument; it should

obtain within 90% of the value within 5 to 10 minutes. Run each concentration for at least 30 minutes. At 0-ppb, the instrument should within 1 or 2-ppb of the offset value that is set on the D/A board.

4. Record the number reached after 30 minutes; if not within at least 90% within 10 minutes, disconnect monitor and troubleshoot for leaks or other possible problems.

What do the numbers mean?

 

1008-PC 400 300 (298) 200 90

1008-RS 370 281 186 82

% 92.5 94.2 93.0 91.1

Here is a table showing what happened from an actual test. Note that the percentages are relatively the same. The 1008-RS ozone monitor passed the system leak test as well as all the span checks and other checks as shown in the manual. The 1008-PC is the reference monitor.

Conclusion: Probably needs a new solenoid valve even though it passes the system leak test. However, don’t hesitate to recheck all connections and settings on the respective instruments and retest just to be sure. 

Rule of Thumb If low readings recorded, but linear

or same percentage difference, it is likely to be a solenoid problem.

If non-linear results recorded at high or low end, then the scrubber is bad.

Miscellaneous Notes The scrubber should have Activated Charcoal, Type F-300, CAS

#7440-44-0.

The practical lower limit of ozone generation for the 1008-PC is a thumbwheel setting of 50-ppb.

Another test against a 1008-PC and another monitor is to set the thumbwheel to a setting of at least a 100-ppb or more. Set the switch to ‘Manual’ and leave the setting at ‘Operate.’ See if the ozone monitors read about the same. The 1008-PC may not necessarily generate 100-ppb in manual mode, but the point of the test is to see how close the instruments read.

Make Sure To:Ideally, you should run the ozone calibration procedure under a lab fume hood.

Make sure to allow each instrument that is checked to warm up for at least an hour.

Complete performance checks (system leak test, lamp frequency, control frequency, etc.) before doing calibration.

With a new scrubber: It is necessary to ‘condition’ the

scrubber by having a high amount of ozone (400 ppb) exposed to it for at least an hour. This will help the ozone monitor have a better response time and a more accurate reading. Only for a new scrubber.

A Discussion of the “offset” It is recommended to operate the

ozone monitors with an offset of ‘9’. The offset is tested by turning on the

monitor and setting the mode switch to ‘Span’. Compare the number to the thumbwheel settings on the ‘D/A Board’.

Offset discussion continued: Make note of the offset before

calibrating in each monitor. If each monitor has an offset of ‘9’,

then you can subtract 9 from each reading for comparison or compare as is. The percent difference will still be the same.