E2638-PID
Rev 10.03.2021
VOC response
The PID can not measure all VOCs or gases, two types of VOCs are not measured:
NR: No response. The lamp does not ionize the VOC and the VOC cannot be measured.
NV: The vapor pressure of the VOC at 20°C is less than a few ppm, so this Semi-Volatile
Organic Compound (SVOC) cannot be measured.
NA: Not available
Occasionally you will be measuring a mixture of VOCs. If the total concentration is within
the linear range of your PID, then it is reasonable to assume that the concentrations are
additive without interference between the different VOCs. Remember that if you are
measuring a combination of VOCs, then the accurate measurement of one of these VOCs
will be difficult; without careful data analysis, you will get only a CF averaged
measurement. Be cautious when reporting actual VOC concentration if you know that there
may be several VOCs present.
Balance gas
The relative response is measured in laboratory air, with 20.9% oxygen, balanced nitrogen.
Some gases absorb UV light without causing any PID response (e.g. methane, ethane). In
ambient atmospheres where these gases are present, the measured concentration of
target gas will be less than is actually present.
Methane absorbs UV strongly, so for accurate measurements in methane containing
atmospheres, calibrate with a calibration gas containing the expected methane
concentration. 50% of LEL methane reduces the reading by up to 50%. Gases such as
nitrogen and helium do not absorb UV and do not affect the relative response.
The correction factor for a gas mix containing PID detectable gases A, B, C… with response
factors RF(A), RF(B), RF(C), in relative proportions a: b: c… is given by:
CF(mix) = 1 / [(a/CF(A) + b/CF(B) + c/CF(C)…]
Accuracy of the Table: This table is for indication only. Table accuracy is 1 to 2 digits only,
so when calculating concentration for a specific VOC, only specify to 1 or 2 digits.
20
Index Chemical name
Alternative name Formula CAS no.
IE, eV
Response
Factor (RF)
10.6 eV
E2638-
PID-40
(ppb)
E2638-
PID-200
(ppb)
1
Acetaldehyde
C
2
H
4
O
75-07-0
10.23
5.5
25
480
2
Acetamide
C
2
H
5
NO 60-35-5
9.69
2
3
Acetic acid
C
2
H
4
O
2
64-19-7
10.66
28
180
3615
4
Acetic anhydride
C
4
H
6
O
3
108-24-7 10.14
4
20
400
