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4-20mA is one of the oldest and most used wired communication protocols out there. These types of sensors are easy to use, easy to set up, reliable, and noise immune. Almost every manufacturing facility will have numerous sensors that output a 4-20mA signal. Generally, these sensors connect to a PLC and from there users have to jump through a few hoops in order to take it to the cloud. There are two ways users can push data to the cloud:
There are two types of 4-20mA signal output devices:
In this article we will be covering the first type, 4-20mA Current Loop ( Active )
4-20mA Current Loop devices are the oldest type of 4-20mA devices. In this type of device, there are two wires. These two wires carry voltage as well as signal. These kinds of devices are also known as 2-wire devices.
These types of devices do not need any external power supply. The NCD transmitter supplies 16V/20mA power.
Product Link: Industrial IoT Long Range Wireless 4-20mA Current Loop Receiver
One of the main reasons behind the popularity of 4-20mA devices is that the hardware setup is extremely simple. Sensors will have two wires. One will be +ve and another one will be Ground.
Power Switch – The switch position should be towards the enclosure wall if it’s powered by internal batteries and it should be away from the enclosure wall if its powered by an external power supply
Radio Module – The antenna cable should be plugged into the radio module. Make sure your modem/gateway radio module looks exactly like the device radio module( same frequency).
Antenna — Antenna should be installed all the time. It should be pointing towards the sky. If possible mount the device away from walls.
M12 connector — This connector contains signal and power wires
“R” Button — Reset Button. When this button is pressed and released devices will send a welcome message followed by a data message
‘C‘ Button — It is a configuration Button.
There are a large number of sensor types that come with 4-20mA output. For example:
All of these sensors can be hooked directly to the ncd.io 4-20mA Current Loop Transmitter Data Acquisition Device.
The ncd.io 4-20mA Current Loop transmitter comes with a high-resolution 16bit ADC and onboard 16V power supply which powers the loop device.
This device is designed to work in low power mode. Here is how it works in the background
The sensor will then send the following data in the Wireless Packet:
Once the hardware is connected, turn on the device and it will send a welcome message followed by a Data message. As an example, let’s say a pressure sensor is connected to the 4-20mA loop transmitter. This pressure sensor can measure pressure between 0-100psi. When the pressure is 0psi the sensor will output 4mA and when the pressure is 100psi it will output 20mA.
7E 00 19 90 00 13 A2 00 41 EE 26 5A FF FE C2 7F 00 03 03 CE 01 00 30 00 32 E4 03 7F 30
Result = ((measured mA – 4mA)/16)* full scale range
As an example, let’s say there is a pressure sensor that can measure 0-50psi and currently outputting is 8mA.
psi = ((8-4)/16)*50
psi = 12.5psi
NCD has built a node-red library for this device. The library can be downloaded using the ncd.io GitHub page.
This flow can be found here:
ncd is always working on improving and enchaining the devices and user experience. Here are the few new features which have been added recently