Node Ethernet/IP Scan List

A small plugin to help with scanning a list of tags.

Installation

npm install --save ethernet-ip-scanlist

or

yarn add ethernet-ip-scanlist

API

ScanTag

The ScanTag class wraps the ethernet-ip tag with the ability to react periodically or to value changes.

ScanTag Constructor

The ScanTag class is constructed with the following parameters:

• tagName: the tag name in the PLC
• vanityName: Description or cleaned-up name (often used for gauges or graphing)
• storePeriod: max number of minutes between periodic value updates. This can be disabled by setting the parameter = 0
• storeChangeDelta: max absolute value change before the value is updated. This can be disabled by setting the parameter = 0

ScanTag.gotValue(value, force=false)

Function to be called when a new value is read by the PLC.

Returns an object { storeValue: <boolean>, reason: <string | null> }

ScanList

The ScanList class holds the configuration and values of all the tags added to the list.

ScanList Constructor

The ScanList class is constructed with the following parameters:

• ipAddress: the IP address of the PLC (it is also possible to pass a FQDN to this parameter)
• slot (optional, default = 0)
• scanRate (optional, default = 200ms): the rate at which the PLC is scanned

add(tagName, vanityName, storePeriod, storeChangeDelta)

Creates a ScanTag with the given parameters.

remove(tagName)

Removes a ScanTag from the ScanList with the given tag name.

Events

Since the ScanList class extends EventEmitter, it has the ability to emit events, two of which have been defined:

1. Updated

The Updated event is emitted by the ScanList class when a tag's value has changed or the tag has been updated by the keepAlive parameter of the tag. This could be a minor change or no change at all. This event is useful for displaying values on an HMI screen or updating an in-memory value.

The event is emitted with a payload of the updated ScanTag.

2. newValue

The newValue event is emitted by the ScanList class when any of the following are true:

• The tag's value has changed by more than the storeChangeDelta
• The amount of time specified in the storePeriod has elapsed
• The force parameter was true when calling gotValue
• There was no previous stored value or timestamp for the tag.

This event is useful for pushing values to a remote monitoring system or storing to a database.

The event is emitted with a payload of the updated ScanTag.

Usage

const { ScanList } = require("ethernet-ip-scanlist");
const scanList = new ScanList("192.168.1.1", 0);
scanList.add("analog_1_value", "Pressure Reading", 1, 60.0);
scanList.add("digital_2_status", "Valve Status (NC)", 1, 0);
scanList.start();
scanList.on("newValue", (tag) => {
    console.log(tag.vanityName, tag.value, tag.lastSendReason);
});