Kappa4413USB – Python Example

Control the 4–20 mA output of an IS4413-M1 current-loop transmitter from your PC, using the Kappa4413USB and a few lines of Python.

flowchart LR
    PC["PC (Python)"] -->|USB| K[Kappa4413USB]
    K -->|I2C| M[IS4413-M1]
    M -->|4–20 mA| L[Current loop]

Loading

The Kappa4413USB shows up on your PC as a serial port. It receives simple text commands over USB and converts them into I2C commands for the IS4413-M1.

What the example does

ISXMPL4413ex2.py:

1. Reads the Kappa4413USB firmware version.
2. Sets the IS4413-M1 power-up current to 0 mA (optional, only needed once).
3. Steps the output through 4, 8, 12, 16 and 20 mA, two seconds each.
4. Sends an out-of-range value (5000) to show how errors reported by the Kappa4413USB are handled.

Requirements

Hardware

• Kappa4413USB
• IS4413-M1
• 24 V supply

Software

• Python 3
• pyserial

pip install pyserial

Quick start

1. Wire the Kappa4413USB, the IS4413-M1 and the 24 V supply as shown in the Kappa4413USB User Manual, and connect the Kappa4413USB to your PC with a USB cable.

2. Find the serial port of the Kappa4413USB. This command lists the available ports:

   python -m serial.tools.list_ports

   On Windows it's a COMx port (you can also check Device Manager → Ports (COM & LPT)). On Linux it's usually /dev/ttyUSB0.

3. Set PORT at the top of ISXMPL4413ex2.py:

   PORT = "COM3"   # Windows: "COM3", Linux: "/dev/ttyUSB0"

4. Run the example:

   python ISXMPL4413ex2.py

From mA to output value

The IS4413-M1 output current is set with a value from 0 to 4095. The example converts mA to output values with a straight line through two points:

VALUE_AT_4MA = 725
VALUE_AT_20MA = 3640

These values are approximate. For the best accuracy, calibrate your unit:

1. Connect a multimeter (mA range) in series with the current loop.
2. Send values with set_value() until the meter reads 4.000 mA, and put that value in VALUE_AT_4MA.
3. Do the same for 20.000 mA and VALUE_AT_20MA.

Serial protocol

The Kappa4413USB uses 115200 baud, 8 data bits, no parity, 1 stop bit (8N1). Commands are ASCII text ending with a newline (\n), and every command gets a one-line reply. A reply starting with ERR means the command failed.

Command	Example	Description
ver	ver	Returns the firmware version number
<value>	2048	Set Current Value: updates the output current (0–4095)
<value>d	0d	Set Default Value: stores the power-up current in the IS4413-M1

Using the class in your own code

The Kappa4413USB class is self-contained. Copy it into your project together with the VALUE_AT_4MA and VALUE_AT_20MA constants, which set_ma() uses:

kappa = Kappa4413USB("COM3")
try:
    print("Firmware version:", kappa.version())
    kappa.set_ma(12)        # 12 mA
    kappa.set_value(2048)   # raw value, 0..4095
finally:
    kappa.close()

Note

Copy the class instead of importing ISXMPL4413ex2.py: importing the file also runs the demo.

Method	Description
version()	Returns the firmware version number
set_value(value)	Sets the output current with a value from 0 to 4095
set_ma(ma)	Sets the output current in mA (the result is limited to 0–4095)
set_default(value)	Stores the power-up current in the IS4413-M1
send(command)	Sends any command and returns the reply
close()	Closes the serial port

send() raises TimeoutError if there's no reply within 1 second, and RuntimeError if the reply starts with ERR. All the other methods go through send(), so they raise the same exceptions.

Troubleshooting

Problem	What to check
TimeoutError: No reply...	The PORT setting and the 24 V supply
could not open port	The port name, and that no other program (a serial terminal, for example) has the port open
RuntimeError: ERR...	The Kappa4413USB rejected the command, for example a value outside 0–4095

On Linux, a permission error usually means your user isn't in the dialout group. Fix it with sudo usermod -aG dialout $USER, then log out and back in.

More information

The Kappa4413USB and the IS4413-M1 are INACKS products. More information at inacks.com.