9 interference gas response, Table 2-1: compatibility of smart block sensors, For example – ENMET OMNI-4000 User Manual
Page 39
OMNI-4000 S/N 6705 and above
ENMET Corporation
33
2.9 Interference Gas Response
Often electrochemical gas detection cells respond to gases other than those they are designed to be specific to. H
2
, for
example, commonly causes a response in CO cells. This response is called "interference." In the OMNI-4000,
compensating circuitry is employed to null out interference signals. On the whole, this compensating circuitry works
well, but it does work better for some combinations of cells than others. The Table 2-1 indicates what can be expected
from exposure of the instrument to possible interfering gases.
Table 2-1: Compatibility of Smart Block Sensors
Interfering Gas Concentration in ppm
Channel
In PPM
O2
CO
300
CO
50
CO
25
H2S
25
H2S
10
SO2
25
NO
50
NO
25
NO2
10
H2
1000
CL2
10
HCN
10
HCL
30
NH3
100
ETO Ethanol
O2
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
CO
*
+/–20
*
+/–5
+/–5
+/–5 +/–10
Incom1 +/–6
/
*
/
*
*
H2S
*
/
/
/
Incom1
/
/
+/–4
/
+/–3
/
*
/
*
*
SO2
*
/
/
/
Incom1
*
/
/
+/–2
/
+/–4
Incom1
*
/
*
*
NO
*
/
/
/
+/–10
*
+/–8
+/–2
/
/
/
*
/
*
*
NO2
*
/
/
/
+/–2
*
/
/
/
/
Incom1
/
*
/
*
*
H2
*
/
/
/
+/–2
*
/
+/–10 +/–10
/
/
/
*
/
*
*
Cl2
*
/
/
/
+/–2
*
/
/
/
Incom1
/
/
*
/
*
*
HCN
*
/
/
/
Incom1
*
Incom1
/
/
+/–5
/
/
*
/
*
*
HCL
*
*
*
*
*
*
+/–1
*
*
*
*
*
*
/
*
*
NH3
*
+/–10
*
+/–10 +/–10
*
+/–10 +/–6
+/–6
+/–5
+/–5
+/–7
+/–4
*
*
*
ETO
*
Incom1 Incom1 Incom1 Incom1 Incom1 +/–4
*
*
*
0
*
*
*
Incom1
O3
*
*
*
*
*
*
*
*
Incom1
*
Incom2
*
*
*
*
*
ClO2
*
/
/
Incom2 +/–1
/
/
Incom1
/
Incom1
*
/
/
*
*
PH3
*
/
/
/
/
/
*
*
/
/
Incom1
/
/
*
*
COCl2
*
/
/
Incom1 Incom1
/
*
*
/
/
/
/
*
*
BRH
*
Incom1 +/–5
+/–8
+/–3
+/–2 +/–10
+/–1
+/–5
/
*
*
/
*
*
* = Not tested
Incom1 = Incompatibility type 1: for the stated concentration, the interference is too high to produce accurate readings.
Incom2 = Incompatibility type 2: for the stated concentration, the interference is too negative to produce accurate
readings.
+/–10 = Some Interference on the indicated channel; Maximum range in ppm given
/ = Limited Interference less than 2% of the interfering gas concentration
For example:
If 25 ppm SO2 is applied to a CO channel, it will cause a maximum signal
equivalent to plus or minus 5 ppm CO.
If the same gas is applied to an H2S channel, it will cause a larger interference signal.
If the same gas is applied to a NO2 channel, it will cause a maximum interference signal of 2% of 25
ppm, which is 0.5 ppm.