Section 5
ZGARD S & DS CO (EC) 4-20mA Output Sensor
Calibration
Calibration Procedure, Electrochemical (EC) 4-20mA Output Carbon Monoxide Sensor:
Perform calibration checks
regularly as part of a routine inspection and maintenance procedure. Use calibration gases of known and certified
concentrations. Check the expiry date on the gas cylinders. The ZGARD S & DS sensor is factory calibrated for 100 or
200ppm Carbon Monoxide, which represents 0 to 100% full scale. The 4-20mA output current between the connection
terminals O/P and COM represents 0 to 100 % full-scale.
U
C
C
A
A
U
U
T
T
I
I
O
O
N
N
The calibration procedure must be completed after the replacement of sensing cells.
Calibration Equipment
Flow controller 0.25 litres/minute and tubing
Purified air as zero gas
60ppm CO in air span gas
Magnetic Strips
*
(Are only used on the ZGARD S Sensors)
Electronic Multi-meter
Calibration Procedure
1.
Disconnect the sensor output from the associated monitoring device. Using a multi-meter, insert two test probes into the
connection terminals labelled O/P & COM.
2.
*
Place the magnetic strips on the top and bottom of the sensor cover plate, ensure the vent holes are fully covered.
U
W
W
A
A
R
R
N
N
I
I
N
N
G
G
Remove the magnetic strips after the calibration has been completed. Otherwise it could fail to perform as designed and
persons who rely on this product for their safety could sustain severe personal injury or death.
ZERO Calibration
3.
Attach a 0.25 l/m., flow controller onto a ZERO gas cylinder. On the ZGARDS S Sensor, insert a calibration adapter into
thread port provided on the protective cover located on the front plate. The ZGARD DS Sensor is provided with standard
calibration adapters.
4.
Connect ¼” Tygon tubing to the outlet of the flow controller, and then slip the open end on the calibration adapter.
5.
Turn ON the flow controller valve and allow the ZERO grade air to quench the sensor for at least 2 minutes.
6.
Adjust the ZERO potentiometer until the current reading is equal to 4mA.
7.
Turn OFF the valve and remove the flow controller from the Zero gas cylinder.
SPAN Calibration
8.
Attach the flow controller onto a SPAN gas cylinder. The SPAN gas should be at least 50% of the sensor’s operating
range.
9.
Turn ON the flow controller valve and allow the SPAN gas to quench the sensor for at least 2 minutes.
10.
Adjust the SPAN potentiometer until the current reading is equal to the calculated value representing the gas
concentration.
SEE:
The example equation below.
11.
Turn OFF the valve and remove the flow controller from the SPAN gas cylinder.
12.
Remove the test hose from the calibration adapter.
13.
Remove the multi-meter test probes from terminals labelled O/P and COM.
14.
Reconnect the sensor output to the associated monitoring device.
Example:
The SPAN gas concentration is
60ppm
Carbon Monoxide in air.
4-20mA is 0-100% F.S., the current that is generated is 16 + 4 = 20mA.
60ppm =
((Span Gas Value x 16) / Full Scale)) + 4
= ((60 x 16) / 100)) + 4 =
13.6mA
5.0
