From the existing A and B values and the measured value Y_o and Y_s and the 0ppm (zero standards) and 25ppm (for
example using 25ppm NH3 standard gas), you can calculate the new value of A and B as below formula.
Ex: We have values
Two calibration points
Standard value
Value read from Sigfox node
1
50
70
2
1000
1100
The old A configuration
1
The old B configuration
0
We have:
A = (1000-50) / (1100-70) = 0.92233
From the formula: Y = AX + B. Then B = Y - AX = 1000 - 0.92233 x 1100 = -14.56311
The new A configuration
0.92233
The new B configuration
-14.56311
As the A and B values are separated values in the memmap of the sensor, we need to use 02 downlink messages to
send to the sensor. Each message will send 1 value of A or B.
For example: A = 1.1 and B = 0.2. Here are the downlink message for setting A & B
Parameter
PRM_ADDRESS
PRM_LENGTH
PRM_VALUE
DOWNLINK_TYPE
Full Downlink
(bytes)
1
1
4
2
8
CONSTANT_A
0x16
0x04 = 4
0x3F8CCCCD = 1.1
0x0005
16043F8CCCCD0005
CONSTANT_B
0x18
0x04 = 4
0x3E4CCCCD = 0.2
0x0005
18043E4CCCCD0005
HIGH_CUT
0x1A
0x04 = 4
0x447A0000 = 1000
0x0005
1A04447A00000005
LOW_CUT
0x1C
0x04 = 4
0x00000000 = 0
0x0005
1C04000000000005
SENSOR_BOOT_TIME
0x1E
0x04 = 4
0x000000C8 = 200
0x0005
1E04000000C80005
SYSTEM_SENSITIVITY
0x32
0x04 = 4
0x41300000 = 11
0x0005
3204413000000005
- Carefully remove the filter;
- Remove the exiting sensor module by using your finger to grip and pull it out;
- Unbox the new sensor in the box;
10.3 Calculate the new value A and B
10.4 Set the new value A and B by Downlink
11. Sensor module replacement:
11.1 Remove old sensor module:
11.2 Install new sensor module:
Summary of Contents for WSSFCB-NH3
Page 9: ...Flow when coming from downlink ...
Page 15: ...BLE broadcast ...
