Section 8
ZGARD S Ammonia (SS) RS485 Output Sensor
Calibration
Calibration Procedure, Solid-Sate (SS) RS485 Output Ammonia 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 1000ppm Rx, which represents 0 to 100% full
scale. The output voltage of 1 to 5Vdc between the test points TPCAL and TPCOM 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 300ppm Ammonia in air span gas
Magnetic Strips
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
test point terminals labelled TPCAL & TPCOM.
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 ¼” Tygon tubing to the outlet of the flow controller, and then slip the open end on the calibration adapter.
6.
Turn ON the flow controller valve and allow the ZERO grade air to quench the sensor for at least 15 minutes.
7.
Adjust the ZERO potentiometer until the output voltage is equal to 1Vdc.
8.
Turn OFF the valve and remove the flow controller from the Zero gas cylinder.
SPAN Calibration
9.
Join the flow controller onto a SPAN gas cylinder. The SPAN gas should be at least 50% of the sensor’s operating range.
10.
Turn ON the flow controller valve and allow the SPAN gas to quench the sensor for at least 15 minutes
.
11.
Adjust the SPAN potentiometer until the output voltage is equal to the calculated value representing the gas
concentration.
SEE: The equation below.
12.
Turn OFF the valve and remove the flow controller from the SPAN gas cylinder.
13.
Remove the test hose from the calibration adapter.
14.
Remove the multi-meter test probes from terminals labelled TPCAL and TPCOM.
15.
Reconnect the sensor output to the associated monitoring device.
16.
Remove Jumper H1-4 to enable the sensor cut-off feature.
Example:
The SPAN gas concentration is 300ppm Ammonia in air.
1 - 5Vdc is 0-100% F.S., the voltage that is generated is 4 + 1 = 5Vdc.
500ppm =
((Span Gas Value x 4) / Full Scale)) + 1
= ((300 x 4) / 500)) + 1 =
3.4Vdc
8.1
