Schneider M340 / Unity Pro - Analog Scaling

[El Miguelo]

Hi,

Is it possible to scale the 4 to 20mA output of a Vegaflex 63 TDR Level Senor mounted on an inclined horizontal cylindrical diesel tank with domed torispherical ends, for volume in litres, by using the dipstick strapping table as a look up table in the M340 using Unity Pro?

I have tried numerous partially filled horizontal cylindrical tank with domed torispherical ends volume formulas but none seem to come close to the dipstick values. The closest I can get is with a 6th order polynomial formula derived from Excel LINEST function but do not know how to apply this to the 4 to 20mA value.

I also not sure of the best configuration of the Vegaflex 63 4 to 20mA output e.g. to use linearization and how to interface this to the PLC.

Regards El

 

[Saffa]

If you've got a formula that works, that can be easily implemented in unity using Structured Text. Just scale the 4-20mA and sensor to give you a reading in whatever units your dipstick uses.

I.e. if the dipstick is in metres with a max of 4m, then set up the the instrument to match and use a scale block to give you a real value in metres. Use this in the formula.

 

[El Miguelo]

The dipstick tables are from 0.04 metres to 4.46 metres in 20mm increments from 4188 litres to 284,550 litres but the curve is not linear. We want the 4 to 20mA signal to indicate the litres in the tank.

 

[Saffa]

Post your linest formula and I'll show you what i mean.

 

[shooter]

yes you can use a table, first start with 2 points (that will give a line, then 3 points and so on until you have enough precision.
when whole table is in you have to use approximation, so find the lower value in the table and the higher one from the measured value. and then get the correct litres from it.
On ships this tables are in a book and for each angle they have separate tables. and factors for weight and temperature.

 

[Lare]

The dipstick tables are from 0.04 metres to 4.46 metres in 20mm increments from 4188 litres to 284,550 litres but the curve is not linear. We want the 4 to 20mA signal to indicate the litres in the tank.

This give only 112 different litre values.
It isn't hard to configure Look up table with these values.

You can calculate approximation linearly from two closest values for level, if more accuracy is needed. (Or if you know exact values, you can add them directly to Look up table.)