A current loop can be modeled with a commonly used equation of a straight line with the form y = mx + b. 4-20mA signals represents a value in 0 - 100% scale.
For Rheonics standard range of viscosity(0-3000cP) this line can be modeled as follows:
y: Instrument Output
x: Instrument Input
Finding m and b:
In our scenario m is calculated as.
b is calculated as the value that intercepts with the y-axis. b is equal to 4.
For a Siemens card 6ES7134-6GD01-0BA1 with a resolution of 16 bits with a range of -32768 to 32,767 ADC counts, the raw value from the PLC must be scaled to real-life measurements. In our scenario, the low limit will correspond to (4mA-0-0cP) and High Limit (20mA-27648-3000cP)