Tip of the Week
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Making Peace with Your Meter
Everyone knows that EPA Method 5 requires the
calibration of the metering system after each field use. We do this either in the field with a
critical orifice, or we send it back to the shop for a check against a wet test
meter.
It is
preferable to do the orifice check in the field for obvious reasons, not the
least of which is to eliminate the specter of having to remobilize a job if the
meter comes back to the shop out of spec.
However, since we don’t normally do an orifice calibration until the end
of the job, we still risk having to repeat a lot of runs and maybe several days
of work if this calibration check fails.
So what can we do to monitor our meter’s performance on an on-going
basis?
There is a
way and it requires practically no effort.
This is the Yqa check, which is described in the ALTERNATIVE METHOD 5 POST-TEST
CALIBRATION (ALT-009), found on the EPA website*.
The trick
is to use the Meter Box Calibration Check section found in lines 45-49 of the
Moisture and Flow tab in the FPS field workbook. Essentially, all you need to do is calculate
the average of the square roots of DH and plug this value into line
47. The workbook will calculate a value
for Yqa (Line 48) and compare this with the Yd of the meter. A deviation of 5% or less between the two is
required (Line 49).
It is a
good idea to keep track of the meter performance during a job by doing this Yqa
check after each run. This will alert
you to potential calibration issues with the meter. Any check that is close to or above the 5%
criteria should be dealt with by either repairing or replacing the meter before
proceeding with additional tests.
*Although the EPA prescribes this as
an alternative calibration procedure, CleanAir’s policy is to always post-test
calibrate our meters using either a critical orifice or a wet test meter. The Yqa-check described here is intended only
to be used as a means of evaluating on-going performance of the metering
system, and is not a replacement of an orifice or bench calibration.