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Appendix C
PID sensor and correction factors tables
EVM Series User Manual
Appendix C
PID sensor and correction factors tables
The following chart details approximate correction factors (or response factors) for specific
concentrations of VOCs.
It is recommended, for best test results, to calibrate the PID sensor with the relevant VOC you intend to
measure. If this is not possible, the factors listed in the table, provided by Ion Science, can be used
when calibrating the PID sensor.
NOTE
: These are approximate values; so, for best accuracy you should calibrate with the relevant
VOC. (Please refer to Ion Science for details on linear range accuracy and table
explanation.)
The table includes six columns
1.
Gas/ VOC
: The most common name for the VOC. If you cannot find the name of your VOC of
concern, refer to Ion Science’s website.
2.
Formula
: To further assist in identifying the VOC, this also is helpful in identifying its molecular
weight, from which ppm measurements can be converted to say, mg/m
3
measurements.
3.
Response Factor
: (RF) also known as
correction factor
. Multiply the output response from the
cell by the RF to provide a normalized scale of VOC concentration.
4.
Relative sensitivity
: (%) This is the inverse of the correction factor, specifying the percent
response of the VOC, relative to isobutylene. If less than 100%, then the VOC is less responsive
than isobutylene; if the relative sensitivity is greater than 100%, then the VOC is more responsive
than isobutylene. Relative sensitivity (%) is specified the same way as cross-sensitivity for toxic
gas sensors.
5.
Typical Minimum Detection Level (MDL) or Minimum Detectable Quantity (MDQ)
: Typical
lowest concentration that can be detected. The Mini PID HI has greater sensitivity than the Mini
PID LO, so MDL’s for the Mini PID HI are much lower. The RF is measured in dry air; high humidity
will reduce this factor by 10% to 20%, so the RF should be increased in high humidity’s.
Attention
: In the table below, a Correction factor listed as “NR” indicates no response since not all
VOCs or gases can be measured with a PID sensor.
NOTE
: The “Typical minimum detection level” is listed in parts per billion in the table below.
The EVM calculates VOCs in parts per million or parts per billion.
Gas/VOC
Formula
(used to convert
ppm measurement
to mg/m
3
)
Correction
factor
Relative
sensitivity (%)
Typical PID
(ppb)
Acetaldehyde
C
2
H
4
O
4.9
21
480
Acetic Acid
C
2
H
4
O
2
36
3
3615
Acetic Anhydride
C
4
H
6
O
3
4.0
25
400
Acetone
C
3
H
6
O
0.7
140
70
Acetonitrile
CH
3
CN
NR
Acetylene
C
2
H
2
NR
APPENDIX
C
