node-red-nodes/function/PID/locales/en-US/pidcontrol.html

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    <p>A PID controller node.</p>
    <p>This node ONLY expects a numeric <code>msg.payload</code> containing the current reading.
    It will output the correction that needs to be applied in order to move to the preset <i>set point</i> value.</p>
    <p>See <a href="https://en.wikipedia.org/wiki/PID_controller" target="_new">Wikipedia</a> for more details.</p>
    <p>The <i>set point</i> may be overridden by <code>msg.setpoint</code>. If you do so the edit box value can be used as the initial value.</p>
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