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pid.js
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/**
* Copyright 2016 Colin Law
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
**/
module.exports = function(RED) {
"use strict";
function PID(config) {
RED.nodes.createNode(this,config);
var node = this;
node.setpoint = Number(config.setpoint);
node.enable = Number(config.enable);
node.prop_band = Number(config.pb);
node.t_integral = Number(config.ti);
node.t_derivative = Number(config.td);
node.integral_default = Number(config.integral_default);
node.smooth_factor = Number(config.smooth_factor);
node.max_interval = Number(config.max_interval);
node.disabled_op = Number(config.disabled_op);
// sanitise disabled output as this is used when all else fails
if (isNaN(node.disabled_op)) {
node.disabled_op = 0;
}
this.on('input', function(msg) {
var newMsg = null;
// Using msg.* to change specific PID property.
if (msg.hasOwnProperty('setpoint')) {
node.setpoint = Number(msg.setpoint);
}
if (msg.hasOwnProperty('enable')) {
node.enable = Number(msg.enable);
}
if (msg.hasOwnProperty('prop_band')) {
node.prop_band = Number(msg.prop_band);
}
if (msg.hasOwnProperty('t_integral')) {
node.t_integral = Number(msg.t_integral);
}
if (msg.hasOwnProperty('t_derivative')) {
node.t_derivative = Number(msg.t_derivative);
}
if (msg.hasOwnProperty('smooth_factor')) {
node.smooth_factor = Number(msg.smooth_factor);
}
if (msg.hasOwnProperty('max_interval')) {
node.max_interval = Number(msg.max_interval);
}
if (msg.hasOwnProperty('disabled_op')) {
node.disabled_op = Number(msg.disabled_op);
// sanitise disabled output as this is used when all else fails
if (isNaN(node.disabled_op)) {
node.disabled_op = 0;
}
}
if (msg.hasOwnProperty('integral_default')){
node.integral_default = Number(msg.integral_default);
}
if (msg.topic == 'setpoint') {
node.setpoint = Number(msg.payload);
} else if (msg.topic == 'enable') {
var wasEnabled = node.enable;
node.enable = Number(msg.payload);
// if now enabled just clear the status, can't do more until a pv sample is received
if (node.enable && !wasEnabled) {
node.status({});
} else if (wasEnabled && !node.enable) {
// now disabled, force the power to the disabled value immediately
newMsg = {payload: node.disabled_op};
node.status({fill:"yellow",shape:"dot",text:"Disabled"});
}
} else if (msg.topic == 'prop_band') {
node.prop_band = Number(msg.payload);
} else if (msg.topic == 't_integral') {
node.t_integral = Number(msg.payload);
} else if (msg.topic == 't_derivative') {
node.t_derivative = Number(msg.payload);
} else if (msg.topic == 'smooth_factor') {
node.smooth_factor = Number(msg.payload);
} else if (msg.topic == 'max_interval') {
node.max_interval = Number(msg.payload);
} else if (msg.topic == 'disabled_op') {
node.disabled_op = Number(msg.payload);
// sanitise disabled output as this is used when all else fails
if (isNaN(node.disabled_op)) {
node.disabled_op = 0;
}
} else if (msg.topic == 'integral_default') {
node.integral_default = Number(msg.payload);
} else {
// anything else is assumed to be a process value
node.pv = Number(msg.payload); // this may give NaN which is handled in runControlLoop
newMsg = runControlLoop();
}
// if there is a message to send then merge in properties from old message as they should be preserved
if (newMsg) {
for (let attrname in msg) {
if (!newMsg.hasOwnProperty(attrname)) {
newMsg[attrname] = msg[attrname];
}
}
}
node.send(newMsg);
});
function runControlLoop() {
//node.log("pv, setpoint, prop_band, t_integral, t_derivative, integral_default, smooth_factor, max_interval, enable, disabled_op");
//node.log(node.pv + " " + node.setpoint + " " + node.prop_band + " " + node.t_integral + " " + node.t_derivative + " " + node.integral_default + " " + node.smooth_factor + " " + node.max_interval + " " + node.enable + " " + node.disabled_op);
var ans;
node.status({});
// check we have a good pv value
if (!isNaN(node.pv) && isFinite(node.pv)) {
// even if we are disabled (enable == 0 or false) then run through the calcs to keep the derivative up to date
// but lock the integral and set power to appropriate value at the end
var time = Date.now();
var integral_locked = false;
var factor;
if (node.last_sample_time) {
var delta_t = (time - node.last_sample_time)/1000; // seconds
if (delta_t <= 0 || delta_t > node.max_interval) {
// too long since last sample so leave integral as is and set deriv to zero
node.status({fill:"red",shape:"dot",text:"Too long since last sample"});
node.derivative = 0
} else {
if (node.smooth_factor > 0) {
// A derivative smoothing factor has been supplied
// smoothing time constant is td/factor but with a min of delta_t to stop overflows
var ts = Math.max(node.t_derivative/node.smooth_factor, delta_t);
factor = 1.0/(ts/delta_t);
} else {
// no integral smoothing so factor is 1, this makes smoothed_value the previous pv
factor = 1.0;
}
var delta_v = (node.pv - node.smoothed_value) * factor;
node.smoothed_value = node.smoothed_value + delta_v
//node.log( "factor " + factor.toFixed(3) + " delta_t " + delta_t + " delta_v " + delta_v.toFixed(3) +
// " smoothed " + node.smoothed_value.toFixed(3));
node.derivative = node.t_derivative * delta_v/delta_t;
// lock the integral if abs(previous integral + error) > prop_band/2
// as this means that P + I is outside the linear region so power will be 0 or full
// also lock if control is disabled
var error = node.pv - node.setpoint;
var pbo2 = node.prop_band/2.0;
if ((Math.abs(error + node.integral) < pbo2) && node.enable) {
integral_locked = false;
if (node.t_integral <= 0) {
// t_integral is zero (or silly), set integral to one end or the other
// or half way if exactly on sp
node.integral = Math.sign(error) * pbo2;
} else {
node.integral = node.integral + error * delta_t/node.t_integral;
}
} else {
//node.log("Locking integral");
integral_locked = true;
}
// clamp to +- 0.5 prop band widths so that it cannot push the zero power point outside the pb
// do this here rather than when integral is updated to allow for the fact that the pb may change dynamically
if ( node.integral < -pbo2 ) {
node.integral = -pbo2;
} else if (node.integral > pbo2) {
node.integral = pbo2;
}
}
} else {
// first time through so initialise context data
node.smoothed_value = node.pv;
// setup the integral term so that the power out would be integral_default if pv=setpoint
node.integral = (0.5 - node.integral_default)*node.prop_band;
node.derivative = 0.0;
node.last_power = 0.0; // power last time through
}
var proportional = node.pv - node.setpoint;
if (node.prop_band == 0) {
// prop band is zero so drop back to on/off control with zero hysteresis
if (proportional > 0) {
power = 0.0;
} else if (proportional < 0) {
power = 1.0;
} else {
// exactly on sp so leave power as it was last time round
power = node.last_power;
}
} else {
var power = -1.0/node.prop_band * (proportional + node.integral + node.derivative) + 0.5;
}
// set power to disabled value if the loop is not enabled
if (!node.enable) {
power = node.disabled_op;
node.status({fill:"yellow",shape:"dot",text:"Disabled"});
} else if (integral_locked) {
node.status({fill:"green",shape:"dot",text:"Integral Locked"});
} else {
node.status({fill:"green",shape:"dot"});
}
node.last_sample_time = time;
} else {
// pv is not a good number so set power to disabled value
power = node.disabled_op;
node.status({fill:"red",shape:"dot",text:"Bad PV"});
}
// if NaN vaues have been entered for params or something drastic has gone wrong
// then set power to disabled value
if (isNaN(power)) {
power = node.disabled_op;
}
if (power < 0.0) {
power = 0.0;
} else if (power > 1.0) {
power = 1.0;
}
node.last_power = power;
ans = {payload: power, pv: node.pv, setpoint: node.setpoint, proportional: proportional, integral: node.integral,
derivative: node.derivative, smoothed_value: node.smoothed_value}
return ans;
}
}
RED.nodes.registerType("PID",PID);
}