User Manual

Global Water Instrumentation

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(ma x) – 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 M ul ti pl i er for Sens or Calibration Settings. EU=Adder+(Multiplier*RawData)

Multiplier = EU(span) / RD(span)

4) Calculate the A d der for Sen sor Cal ibr ati on Settings.

Adder = - (Multiplier x RD(min)) + EU(min), observe polarity

Example 1: 4-20mA, 0-10 0 M PH Wi nd 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 = - (Multip li er x RD(min)) + E U (min) = - (0.123153 x 205) + 0 = - 25.2463

Example 2: 4-19mA, -50°C - +50°C Temperature sensor, °F. Raw( 4m A) =2 04, Ra w ( 19m A) =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) = 3.846m A @ -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(mi n)) + EU(min) = - (0.232558 x 196) + (-58) = -103.5814