Xylem SIT65 SATELLITE INTERNET TELEMETRY - Manual (Page 20)

Global Water Instrumentation
20
Appendix B: Adder and Multiplier Numbers
1) Define the Engineering Units (EU) and span (0 to 100 MPH, -50°C to +50°C, etc).
EU(min) = Minimum EU corresponding to minimum sensor output
EU(max) = Maximum EU corresponding to maximum sensor output
EU(span) = EU(max) – EU(min), observe polarity
2) Calculate the Raw Data (RD) span.
For 4-20mA Current Output Sensors:
I(min) = Sensor output current @ EU(min)
I(max) = sensor output current @ EU(max)
RD(min) = I(min) / 4 x Raw(4mA), round down to nearest integer
RD(max) = I(max) / 19 x Raw(19mA), round up to nearest integer
RD(span) = RD(max) – RD(min)
Raw(4mA) and Raw(19mA) are provided on the Configuration Report
For 0-5VDC Voltage Output Sensors:
V(min) = Output voltage @ EU(min)
V(max) = Output voltage @ EU(max)
RD(min) = V(min) / 5 x 1023
RD(max) = V(max) / 5 x1023
RD(span) = RD(max) – RD(min), Round Off
3) Calculate the Multiplier for Sensor Calibration Settings. EU=Adder+(Multiplier*RawData)
Multiplier = EU(span) / RD(span)
4) Calculate the Adder for Sensor Calibration Settings.
Adder = - (Multiplier x RD(min)) + EU(min), observe polarity
Example 1: 4-20mA, 0-100 MPH Wind Speed sensor. Raw(4mA)=205, Raw(19mA)=972
EU(min) = 0 MPH EU(max) = 100 MPH
EU(span) = EU(min) – EU(max) = 100 – 0 = 100 MPH
I(min) = 4.004mA @ 0MPH I(max) = 19.884mA @ 100MPH
RD(min) = 4.004 / 4 x 205 = 205.2 ≅ 205
RD(max) = 19.884 / 19 x 972 = 1017.2 ≅ 1017
RD(span) = RD(max) - RD(min) = 1023 – 204 = 812
Multiplier = EU(span) / RD(span) = 100 / 812 = 0.123153
Adder = - (Multiplier x RD(min)) + EU(min) = - (0.123153 x 205) + 0 = - 25.2463
Example 2: 4-19mA, -50°C - +50°C Temperature sensor, °F. Raw(4mA)=204, Raw(19mA)=971
EU(min) = -50°C = -58°F, EU(max) = +50°C = 122°F, [°F = (°C x 9 / 5) + 32]
EU(span) = 122°F – (-58°F) = 180°F
I(min) = 3.846mA @ -58°F, I(max) = 18.988mA @ 122°F
RD(min) = 3.846 / 4 x 204 = 196.1 ≅ 196
RD(max) = 18.988 / 19 x 971 = 970.4 ≅ 970
RD(span) = EU(max) – EU(min) = 972 – 196 = 774
Multiplier = EU(span) / RD(span) = 180 / 774 = 0.232558
Adder = - (Multiplier x RD(min)) + EU(min) = - (0.232558 x 196) + (-58) = -103.5814