Met One Instruments BX-302 Zero Filter Calibration Kit Instruction Manual

The BX-302 Zero Filter Calibration Kit is used to audit or adjust the background (BKGD) value on Beta Attenuation Monitors (BAM) particulate monitors. Follow these instructions carefully for optimal accuracy.

The BX-302 may come with a cover for protection during use.
The BKGD value is the zero correction used for BAM instruments and should be verified or adjusted during initial field deployment and audited seasonally or annually.

Perform the zero test in stable environmental conditions to avoid measurement errors.
Always use the included BX-302 cover during background testing to prevent interference from water or sunlight.

Refer to the specific BAM instrument’s manual for detailed background test procedures.

BX-302 Zero Filter Kit Manual – © Copyright 2007 Met One Instruments, Inc. All Rights Reserved worldwide.
No part of this publication may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any other language in any form without the express written permission of Met One Instruments, Inc.

Overview

This document describes the procedure for using the BX-302 Zero Filter Calibration Kit to audit or adjust the background (BKGD) value on the BAM-1020 particulate monitor.
These instructions must be followed carefully to obtain the best accuracy from the unit.

Refer to the BAM-1020 operation manual for more information.

About the Background

The Background (BKGD) value is the zero correction (slope offset) for all BAM-1020 concentration data. This is determined by running the unit for two to three days with a HEPA zero filter installed on the inlet so that no particulate enters the instrument. The concentration data values over this time are averaged, and the BKGD value is the negative of this average. All of the subsequently stored concentration data contains this correction. The BKGD value varies from unit to unit and is typically a number between +0.001 and -0.005 mg/m3. Warning: This is a user-settable calibration value that may significantly affect the accuracy of the unit.
The BKGD value is factory-calibrated for each BAM-1020 under laboratory conditions. Units configured as PM2.5 or PM10-2.5 FEM monitors must have this value verified and/or adjusted by the user during the initial field deployment of the instrument, using the BX-302 zero filter kit. For PM10 units, the BKGD value may optionally be tested and adjusted for best accuracy, though it is not technically a requirement. The BKGD value should also be audited either seasonally or at least annually afterward.

This field zero test corrects the BKGD value to compensate for minor variations caused by local conditions such as inlet heater operation, grounding, RFI/EMI, and shelter temperature control characteristics. It is not uncommon for the initial field zero test to result in a BKGD value that varies from the factory-set value by up to several micrograms. Subsequent field zero tests should usually result in the BKGD value staying consistent within about 1ug.
If possible, the zero test should not be performed during a period of rapidly changing barometric pressure. The room air temperature also should not change rapidly from hour to hour during the test. This is because changes in air density can be measured as mass noise, and may adversely affect the test results. Shelter temperature changes of 2 degrees C or less between the beginning and the end of each sample hour are usually considered acceptable. The exact shelter temperature is not important, as long as it remains fairly constant.

Equipment Required

BX-302 Zero Filter Calibration Kit.
Fully installed and operational BAM-1020 monitor.

Computer with Comet or HyperTerminal communication software, a spreadsheet program such as Microsoft Excel® , and a BAM-1020 serial communication cable.

Test Setup

The BAM-1020 should be installed in its normal shelter at the field site where sampling is to be performed.

The unit must be configured for normal operation in its usual environment. The BAM-1020 and especially any shelter temperature control system should ideally be powered up for about one day before starting the zero test, or the first day of data after power-up can be ignored. This allows the temperatures in the BAM and the shelter to equilibrate to a stable state for optimal accuracy and stability.
The Smart Inlet Heater must be installed and operating normally. It must be set for the normal control parameters per the BAM-1020 manual, such as the normal RH setpoint of 35%.

Remove the PM10 and PM2.5 inlets, and install the BX-302 zero filter assembly onto the top of the inlet tube as shown above. Install the white plastic sun/rain shield by screwing it onto the filter. This keeps rain out of the filter and shades it to help prevent condensation from forming inside. Note: The 90-degree nylon inlet fitting and short length of clear tubing that used to be supplied with the filter kit is no longer recommended since it does not reliably keep moisture out of the filter under some conditions.
As an alternative setup, the zero filter may be installed inside the BAM shelter, on a short inlet tube just above the smart heater. In any case, the inlet heater must be installed and running normally.

The BKGD (Background) value is located in the SETUP > CALIBRATE menu. Record the previous BKGD value, then change it to 0.0000, so that the BAM is not performing any background corrections during the test. This simplifies the math and reduces mistakes. Exit back to the main menu.

Leak Check
A leak check must be performed before proceeding with the Background test. Leaks at the nozzle can appear as background noise or a data offset. See the BAM-1020 manual for more information on the leak check, nozzle cleaning, and leak repairs. Perform the following steps to check for leaks:

Clean the sample nozzle and tape support vane (located under the filter tape) with isopropyl alcohol and cotton-tipped applicators as described in the BAM-1020 manual.
Turn the leak check valve on the BX-302 filter to the OFF position (handle perpendicular to the valve body) to prevent any air from entering the inlet tube.

In the TEST > PUMP menu, turn on the pump. The flow rate should drop below 1.0 L/min. If the leak value is 1.0 L/min or greater, then the nozzle and vane may need cleaning, or there may be another leak in the system.
Resolve the leak and perform the check again. A properly functioning BAM will usually have a leak value of about 0.5 L/min with a clean nozzle and vane using this method.
Turn the pump off and exit to the main menu. Open the valve on the BX-302 (handle parallel to the valve body).

Background Test Process

After the warm-up period, start the BAM sampling for about 72 hours. The unit should be operating just like it would for regular PM2.5 sampling, only with the zero filter installed instead of the PM10 inlet and cyclone.
After at least 72 hours of sampling, download the hourly concentration data from the unit (.csv output per the manual) using Comet or HyperTerminal and import it into Excel for analysis. An Excel template to expedite the zero test data evaluation (shown below) is available from Met One Instruments.
The data should not contain error flags during the test period. Investigate any errors.
The first four hours of data may optionally be discarded and the remaining hours used for analysis. This sometimes improves the data set because of the tape tracking for the first few hours, if not perfectly centered when installed.
Graph the concentration data. The zero noise levels of the BAM-1020 from the test will be visible. The example below shows a typical zero data set from a BAM-1020.
Calculate the average of the zero data to four decimal places. Calculate a new BKGD value for the unit by taking the negative of the average. For example, on the data below the average of the zero data was +0.0016 (+1.6g), so the correct new BKGD value is -0.0016 (-1.6g). Enter the new BKGD value into the BAM in the SETUP > CALIBRATE menu. Note: Be careful to observe the decimal point position, because the BKGD value in the BAM is always entered in milligrams, not micrograms.
Compare the new BKGD to the previous BKGD value recorded before the test. The two values should usually be similar within a microgram or two. If the values are considerably different, check the BAM for leaks at the nozzle and verify the temperature stability of the shelter. Note: The initial field BKGD value will often be several micrograms different than the factory value because the factory value is set without an inlet heater.
Calculate the standard deviation of the data (STDEV function in Excel) to four decimal places. This value varies from unit-to-unit, but should usually be less than 2.4 micrograms. The lower the number, the better the noise characteristics. A large standard deviation of noise is a clue that the test data average may not be ideal for setting a new BKGD correction. Noisy data should be investigated and resolved. Check for BAM or inlet tube grounding problems, leaks, zero filter condensation, close RFI or EMI sources, large changes in shelter temp or pressure, improper filter RH control, etc. Excessive noise can also indicate a failing beta detector.
Make a record of the test results and any BKGD value changes, and keep it with the other calibration records for the BAM-1020. The Met One Excel template shown below can serve as a good test record.
After the test, remove the BX-302 filter and reinstall the PM10 and PM2.5 inlets. Resume normal operation.

CONTACT

Met One Instruments, Inc

1600 Washington Blvd.

Grants Pass, Oregon 97526
Telephone 541-471-7111
Facsimile 541-541-7116

FAQ

Q: How often should the BKGD value be audited?
- A: The BKGD value should be audited either seasonally or at least annually after the initial field deployment.
Q: What should be done if the zero test results vary significantly from the factory-set value?
- A: In case of significant variations, recalibrate the BKGD value using the BX-302 Zero Filter Calibration Kit following the provided instructions.
Q: Can the zero test be performed in any environmental conditions?
- A: It is recommended to perform the zero test in stable environmental conditions to avoid measurement errors influenced by rapid changes in air density.

Documents / Resources

Met One Instruments BX-302 Zero Filter Calibration Kit [pdf] Instruction Manual
BX-302 Zero Filter Calibration Kit, BX-302, Zero Filter Calibration Kit, Calibration Kit, Kit

References

User Manual

Met One Instruments BX-302 Zero Filter Calibration Kit

Product Information

Product Usage Instructions