Section 4
ZGARD S CO (SS) 4-20mA Output Sensor
Calibration
Calibration Procedure, Solid-State (SS) 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 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 labeled
4-20mA output 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 and 60ppm CO in air span gas
Magnetic Strips
Electronic Multi-meter
Container of Distilled water with inlet and outlet tubing, required for humidifying the calibration gas.
REFER: to Drawing
106894B.
Calibration Procedure
1.
Disconnect the sensor output from the associated monitoring device. Using a multi-meter, insert test probes into the
connection terminals labelled O/P & COM.
2.
Insert Jumper H1-4 to disable the sensor cut-off feature.
3.
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
4.
Join a 0.25 l/m., flow controller onto a ZERO gas cylinder. Insert a calibration adapter into thread port provided on the
protective cover located on the front plate.
5.
Connect the ¼” Tygon tubing between the inlet of the gas humidification assembly and the calibration cylinder flow
controller outlet port.
6.
Connect the outlet tubing of the gas humidification assembly to the sensor calibration adapter.
7.
Turn ON the flow controller valve and allow the ZERO grade air to quench the sensor for at least 15 minutes.
8.
Adjust the ZERO potentiometer until the current reading is equal to 4mA.
9.
Turn OFF the valve and remove the flow controller from the Zero gas cylinder.
SPAN Calibration
10.
Join the flow controller onto a SPAN gas cylinder. The SPAN gas should be at least 50% of the sensor’s operating range.
11.
Turn ON the flow controller valve and allow the SPAN gas to quench the sensor for at least 15 minutes.
12.
Adjust the SPAN potentiometer until the current reading is equal to the calculated value representing the gas
concentration
. SEE: The equation below.
13.
Turn OFF the valve and remove the flow controller from the SPAN gas cylinder.
14.
Remove the test hose from the calibration adapter.
15.
Remove the multi-meter test probes from terminals labelled O/P and COM.
16.
Reconnect the sensor output to the associated monitoring device.
17.
Remove Jumper H1-4 to enable the sensor cut-off feature.
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
4.0
