# Distance measurement to liquid plastic

What's the best way to find out how much plastic I got in a container?

Characteristics:

• It's slimey
• It's liquid
• It's sticky
• Its electrical resistance is very very high
• It's very warm(250 degrees celsius)
• Sometimes it will be see-through plastic and sometimes it will be a very thick plastic with a strong color.

Extra information:

I will use a cylinder to suck X liquid plastic from the container and pour it into shapes, and I got a feeder with resin which will pour into the container. And I don't know how I'm going to tell the feeder when to feed the container because I don't know how to tell how much plastic there is in the container.

So the distance measurements doesn't have to be precise, it can be binary. As long as it works.

• Do you want to know the volume of plastic in the container? Or the distance between two things? (if the latter, exactly what surface to what surface) – Oli Glaser Sep 2 '12 at 23:41
• volume, weight, anything. Distance from the surface of the liquid to.. whatever I can put above it, so be it 5cm above or 30cm above. – Harry Svensson Sep 3 '12 at 0:46

You could try to measure the weight of the container, using rather simple pressure sensors for example.

• I do like this idea – Harry Svensson Sep 3 '12 at 0:46

If you know the cylinders volume, then you can use this to calculate the amount dispensed, and also weight if you know the weight/volume relationship of the plastic.

I don't know what type of "cylinder" it is or how the plastic gets in and out of it, but I imagine some hacking with a stepper motor and rotary encoder could dispense the plastic and get you the required information to be processed by the uC.
Alternatively, there are plenty of dispensing pumps around for all types of liquids/volumes/precisions, some that will come with measurement outputs, but these can get quite expensive.

Weighing the container (as suggested by Turbo J) is another option, again how useful depends on your setup. A wheatstone bridge 2 or 4 load cell setup (could be taken from a digital scale) could be used. You can then calculate volume from the weight.

For distance to surface of liquid, ultrasound or IR distance sensor could be used.

• Using an ultrasound sensor seems the right way to me, if weight is not possible. But with an IR distance sensor, it could be a problem that the color of the material is changing, and sometimes transparent - and hot too. – Volker Siegel Aug 3 '14 at 15:49