Model B12-69 Wet Oxidant Gas Transmitter
O & M Manual
- 15 -
Rev-G, 7/15
CALIBRATION
Transmitter calibration requires adjustment of both zero and span. Zero is adjusted when the
sensor is exposed to air containing no oxidant gases. Span is adjusted when a gas stream containing a
known concentration of oxidant gas is passed through the low volume flowcell.
ZERO ADJUSTMENT
As previously mentioned, adjusting the transmitter zero requires that the sensor be exposed to
oxidant gas free air. The simplest approach is to simply expose the sensor to ambient air that is free of
gases to which the sensor will respond. Threading the low volume flowcell onto the sensor will isolate the
sensor from surrounding air for zeroing purposes.
If the area in which the sensor is operating is known to be gas free, then the transmitter can be
zeroed without further equipment. If not, use of “zero air” from a gas cylinder is recommended. Zero air
is available as part of all ATI calibration kits, or may be obtained from any specialty gas supplier. When
zero air is to be used, a low volume flowcell (part no. 00-0422) must be used. The low volume flowcell
provides a confined space around the sensor into which the zero air can flow. The flowcells provide tube
fittings at the bottom to connect air tubing as shown in Figure 2.
To zero the transmitter, remove the cover and connect a DVM to the test points shown in Figure
6. Observe the DVM value to be sure that it is no longer declining, and that it is stable ± 4 mv. Use the
zero potentiometer (Figure 6) to adjust the test point voltage to 0.040 VDC (40 mv.). If the transmitter is
supplied with the LCD option, no DVM is required.
SPAN ADJUSTMENT
Once the zero has been set, slide the low volume flowcell onto the sensor (if it is not already
there from zeroing). Attach a source of gas with a know chlorine gas concentration and adjust the sample
flowrate to 500 cc/min. A typical chlorine gas source is the electrochemical chlorine generator
manufactured by Advanced Calibration Designs in Tucson, AZ. Allow sample to flow for 10 minutes.
Observe the DVM value. The reading should be relatively stable ±4 mv. Adjust the span
potentiometer (Figure 6) until the proper test point voltage is obtained. The proper voltage to set when
adjusting transmitter span will vary depending on the range of the transmitter. The following formula is
used to calculate the proper span voltage for any transmitter.
V = 0.040 V + [0.160 X (Measured Concentration ÷ Transmitter Range)]
As an example, suppose you are calibrating a transmitter with a range of 0-10 PPM, and the
chlorine gas standard used for calibration has a value of 5 PPM. The above formula would then become:
V = 0.040 V + [0.160 X (5 ÷ 10)] = 0.120 V.
Therefore, adjusting the transmitter to a reading of 120 mv. at the test point would properly
calibrate the transmitter.
NOTE:
The response of a wet gas sensor is 1:1 for chlorine, bromine, or iodine. The chlorine dioxide
response is approximately 0.7:1, meaning that the gas standard value in the above equation must
be multiplied by 1.4 to arrive at the correct calibration value.
