PR55-5A Analog to Current Formula

spscogg · April 13, 2023, 1:52pm

Can you elaborate on how the below formula is derived for converting analog value to mA? I get a different value when calculating 0-20mA range, 15 bit resolution.

mA = raw_adc * 0.0006934

TravisE_NCD_Technica · April 13, 2023, 2:51pm

Are you writing your own software/script to parse the data received from the PR55-5A? What language are you developing in?

You can take a look at the parsing code for the type 45 sensor here(line 1854):

github.com

ncd-io/node-red-enterprise-sensors/blob/main/lib/WirelessGateway.js

const events = require('events');
const Queue = require('promise-queue');
globalDevices = {};
module.exports = class WirelessSensor{
	constructor(digi){
		this.mac;
		this.digi = digi;
		this.send = digi.send;
		this._emitter = new events.EventEmitter();
		this.sensor_pool = {};
		this.sensor_types = sensor_types(this);
		this.queue = new Queue(1);
		this.payloadType = {
			'122': 'power_up',
			'124': 'config_ack',
			'125': 'config_error',
			'127': 'sensor_data'
		};

		var that = this;

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spscogg · April 13, 2023, 6:34pm

I am using python. Just trying to understand the conversion from ADC reading to mA.

0-32767 15-bit adc
0-20mA measure range
20/32767=0.0006104 resolution
However, the formula in the manual shows 0.0006934?

It’s a small difference, but it is somewhat significant difference once I interpolate the mA reading to process value.

Anil_Bhaskar · April 13, 2023, 6:38pm

The true range is around 0-22mA. There is +/-2% tolerance.