Month: March 2019

Node-Red ~ Modbus Floating Point Convert (Float32 / Real)

29Mar

this function script is used to convert your 2 words into Float32bit

/* Converts from an number, string, buffer or array representing an IEEE-754 value
 to a javascript float.
 The following may be given in msg.payload:
 A string representing a number, which may be hex or binary
 examples, "1735" "0x02045789" 0b01000000010010010000111111011011
 An integer value
 A two element array or buffer of 16 bit values, less significant byte first.
 A four element array or buffer of 8 bit values, most significant byte first.
 Source: https://flows.nodered.org/flow/359ead34237b7ab6ec0465ee85a34b62
 */
 // first make a number from the given payload if necessary
 let intValue;
 if (typeof msg.payload === "number") 
{
 intValue = msg.payload;
 } else if (typeof msg.payload === "string") {
 intValue = Number(msg.payload);
 } else if (msg.payload.length == 2) {
 // two int array or buffer
 intValue = (msg.payload[1] << 16) + msg.payload[0];
 } else if (msg.payload.length == 4) {
 // four byte array or buffer
 intValue = (((((msg.payload[0] << 8) + msg.payload[1]) << 8) + msg.payload[2]) <<
 8) + msg.payload[3];
 } else {
 node.warn("Unrecognised payload type or length");
 } 
 msg.payload = Int2Float32(intValue);
 msg.payload = msg.payload.toFixed(1);
 return msg;
 function Int2Float32(bytes) {
 var sign = (bytes & 0x80000000) ? -1 : 1;
 var exponent = ((bytes >> 23) & 0xFF) - 127;
 var significand = (bytes & ~(-1 << 23));
 if (exponent == 128)
 return sign * ((significand) ? Number.NaN : Number.POSITIVE_INFINITY);
 if (exponent == -127) {
 if (significand === 0) return sign * 0.0;
 exponent = -126;
 significand /= (1 << 22);
 } else significand = (significand | (1 << 23)) / (1 << 23);
 return sign * significand * Math.pow(2, exponent);
 }