P4441 Stream

This is a Duplex Stream implementation used to facilitate access to p4441 or rather the noise monitoring terminals. At it's heart is a socket, however, it handles all of the statefulness from Brüel & Kjær's analyzer interface.

The primary use of this stream is to simply get the NMT to enter its real-time dB flow mode. Many things can go wrong along the way, and users of the interface only care about reading and writing data, not the various outputs of the interface.

Install

npm install p4441-stream

Usage

This module exports a contstructor for this stream object, but also exposes a factory function as a property on the constructor.

var nmt = require('p4441-stream');

var leqStream = nmt.getLeqStream({
  address: 'localhost'
, port:     10001
, password: 'my-password'
});

// `data` emits raw data stream from socket
// => 44.7, 45.3, 44.9...
leqStream.pipe( process.stdout );

// `leq` emits parsed data
leqStream.on( 'leq', function( leq ){
  assert( typeof leq === 'number' );
});

// Optional callback
leqStream.connect( function( error ){
  /* You may handle errors in callback or in `error` events */
});

Static

getLeqStream( object nmt )

Equivalent to running:

var Nmt = require('p4441-stream');
var nmt1 = new Nmt();

Methods

setNmt( object nmt )

Sets the NMT object if one did not pass the value into the factory function.

connect( callback )

Calls connect on the underlying source socket. Will callback with callback( error ). Also emits connected. Once connected, the stream will call login and then enterRealTime since we assume that the user simply wants to put the NMT in flow mode, this method takes care of everything.

login( callback )

Attempts to login to the NMT. Depending on the current state, it will write nmt.password to the underlying socket. Once a proper response comes back, it will callback with callback( error ). If the socket emits a chunk containing an *, then we know the password was incorrect and we emit an error; If the socket emits a chunk containing a $, then we know that either the login was successful or we were already logged in.

logout( callback )

Attempts to logout of the NMT. Depending on the current state, it will write logout to the underlying socket. Once a proper response comes back, it will callback with callback( error ). If the socket emits a chunk containing an *, then we know it was successful.

enterRealTime( callback )

Attempts to get the NMT in dB flow mode by writing level repe to the underlying socket. Emits: reading-leqs, and entered-real-time.

Events

• error
• data
• leq
• end
• close
• transaction-complete
• transaction-begin
• entered-real-time
• invalid-password
• reading
• at-login
• at-prompt
• reading-leqs

While this module emits standard data events you would expect from a stream, it also emits a more useful leq that is pre-parsed. So you're not getting the strings straight from the wire (like the data from the console interface and pressurized leq readings in the real-time flow mode).