Calculator for 4-20mA Signal to 1- 5Volt and PLC 16-bit Raw Count Values
The converter calculation involves converting analog signals, such as 4-20 mA currents, to meaningful digital values for a PLC’s 16-bit analog-to-digital converter.
For 4-20 mA to 1-5 volt conversion, the input current is mapped to an output voltage within a defined range. Then, the voltage is scaled to fit the 16-bit ADC range, accounting for both unsigned (0-65535) and signed (-32768 to 32767) representations.
A scaled voltage is calculated and translated to raw count values. For signed values, a midpoint adjustment ensures proper representation. This process ensures accurate data conversion for sensors or measurements into values usable by PLC systems.
Formula for the calculation
Let’s try converting a 4-20 mA current signal to a 1-5 volt signal and then finding out the matching PLC 16-bit raw count values for both signed and unsigned formats.
Step 1: Convert 4-20 mA to 1-5 Volt
Assuming you have a current signal (I) in the range of 4 to 20 mA and you want to convert it to a voltage signal (V) in the range of 1 to 5 volts.
Here’s the formula:
V=Vmin+{(I-Imin)/(Imax-Imin)} X (Vmax-Vmin)
Where
V is the output voltage in volts (between 1 and 5 volts)
I is the input current in mA (between 4 and 20 mA)
Vmin is the minimum output voltage (1 volt)
Vmax is the maximum output voltage (5 volts)
Imin is the minimum input current (4 mA).
Step 2: Convert 1-5 Volt to PLC 16-bit Raw Count Value
Assuming your PLC has a 16-bit analog-to-digital converter (ADC) with a range of 0 to 32767 counts.
Unsigned Range
An unsigned 16-bit ADC can represent values from 0 to 65535 (216-1)
The formula to calculate the raw count value (RC) is:
RC=(V/Vmax) x (216-1)
Where
V is the voltage signal in volts (between 1 and 5 volts).
Vmax is the maximum voltage in volts (5 volts).
(216-1) is the maximum count value for a 16-bit PLC ADC (65535 for unsigned).
Signed Range
A signed 16-bit ADC can represent both positive and negative values. It uses a technique called two’s complement representation. The range for a signed 16-bit ADC is from -32768 to 32767.
When you’re converting an analog signal to a raw count value for a signed 16-bit ADC, the key is to understand how the signal’s voltage range maps to this signed range.
Let’s consider the conversion of a voltage signal V to a raw count RC (signed) for a PLC’s signed 16-bit ADC with a range of -32768 to 32767:
RC=(V/Vmax) x {(216)- (215)}
V is the voltage signal in volts (between 1 and 5 volts).
Vmax is the maximum voltage in volts (5 volts).
(216) is the maximum count value for a 16-bit PLC ADC (65535).
(215-1) is half of the total count range, which accounts for the signed range split.
Example calculation
Conversion to Voltage
Input Current (I) = 12 mA
Using V = 1+ {(12-4)/20-4)}x (5−1)
Calculated Voltage (V) = 3 Volts
Conversion to Raw Count (Unsigned)
Using RC (unsigned) = (⅗) x (216-1)
RC (unsigned) = (⅗) x 65535
Calculated Unsigned Raw Count (RC) ≈ 39321
Conversion to Raw Count (Signed)
Using RC (signed) = (⅗) x(216)-(215)
RC (signed) = (⅗)×(65536−32768)
Calculated Signed Raw Count (RC) ≈ 19661
In this example, a 12 mA current is converted to 3 volts and then scaled to raw count values for a PLC. The unsigned raw count is approximately 39321, and the signed raw count is approximately 19661.
4-20mA Signal To 1- 5Volt And Plc 16-bit Raw Count Values Calculator
The below calculator used to calculate 4-20mA signal To 1- 5volt and PLC 16-bit raw count values