Xytronix Research & Design ControlByWeb X-16s User Manual page 14

Example Applications
3.2 Monitor Flow, Distance, or Speed with a 4-20mA Sensor
Signal conditioners are available for measuring flow, distance, speed and many other industrial
processes. Many popular signal conditioners employ a 4-20mA analog output. With a simple shunt
resistor these transducers can be connected directly to the X-16s as described in Section 2.4.1 above.
Once the components are properly wired, the X-600M must be configured with the proper Slope and
Offset to convert the voltage measurement into engineering units such as CFS (flow), Meters (distance)
or Meters per Second (speed). For linear transducers this is normally done with a Y=mX+b equation.
Engineering Value = (Measured Value * Slope) + Offset
The documentation for the sensor must be consulted for the calculations. For example, if the range of a
laser rangefinder is 1Meters to 100Meters the transducer will output 4mA at 1M and 20mA at 100M. By
default the X-16s makes measurements in units of Volts. To convert this measurement to engineering
units the voltage measurement must be processed with a Slope setting. The general term for the Slope
is:
Slope = (Y2-Y1)/(X2-X1)
To determine the slope, first determine the minimum and maximum voltage range that will be applied to
the X-16s. In this example the transducer will output 4mA at 1M and 20mA at 100M. This can be
converted to voltage using Ohms Law V=IR.
Vmin = 4mA * 250 Ohms = 1V
Vmax = 20mA * 250 Ohms = 5V
To calculate the slope:
Slope = (100M – 1M)/(5V – 1V) = 24.75 Meters/Volt
Once the slope is determined, calculate the offset using the Y=mX+b linear equation where b is the
offset.
1M = 24.75M/V * 1V + Offset
Offset = 1M – (24.75M/V * 1V) = -23.75M
Configure the X-600M with the new settings as shown in Section 2.4.
Page 14
X-16s™ Users Manual
Xytronix Research & Design, Inc.