scaleLinear help

Help
1

As in the example for scaleLinear:

{{scaleLinear 0 100 0 10000 10}} returns 1000 because 10 is 10% of 100, therefore 10% of 10000 is 1000.

So therefore should {{scaleLinear 4000 20000 0 300 8000}} not output 150 ? as 8000 is 50% of 16000( 4000 to 20000 = 16000) , but instead I get 75.

Im using a 4-20mA pressure sensor, so a span of 16mA( min to max ) should scale to a tank depth( 0 to 300 cm ) should it not ?

2

{{scaleLinear}} takes the final argument (the value to scale) and maps it from its original domain (the first two arguments) to its new domain (the third and fourth arguments).

So, given …

{{scaleLinear 4000 20000 0 300 8000}}

8000 is 25% of the way up the scale from 4000 to 20000 - as in …

  • A value of 4000 would be 0% (bottom of scale)
  • A value of 20000 would be 100% (top of scale)
  • A value of 12000 would be 50% (halfway between 4000 and 20000)

So, when you go 25% of the range from 0 to 300, that gives you 75.

As a mathematical equation, you can think of {{scaleLinear}} as doing the following …

scaledValue = (originalValue - fromLow) * (toHigh - toLow) / (fromHigh - fromLow) + toLow
3

So Im better off usinig 8000/(20000-4000)=50%

4

Well, does a reading of 4000 mean your tank is empty (at 0 cm) and a reading of 20000 mean your tank is full (300 cm)? And do those readings scale linearly with the tank depth?

5

Yes its a 4-20mA pressure senor so 4000 is empty and 20000 is full. The depth of the tank varies so I’ve been using:

{{scaleLinear 4000-20000 0 TANK DIAMETER SENSOR_mA OUTPUT}} expecting a depth