Hi people,

I need to design a circuit which is able to measure pressure, and when a certain pressure is reached, a relay is activated. The pressure I need to measure is pressure between two surfaces (the force between the two plates rather then pressure).

Can anyone give me some clues on what type of gauges I should use and some hints how to design my circuit?

Thanks everyone,

 

One possibility would be some sort of strain gage on the plates. If it is a press (as in hydraulic press), the usual way is to measure pressure in the hydraulic fluid.

You need to give more information about how you are creating the pressure, the magnitudes of forces/pressure you need to measure, and other design factors. John

 

Thanks John for your reply.

First of all, I need this circuit because I need to measure the force excerted by a clamp on an object.
The first thing I had in mind was a strain gauge, as you mentioned, but my problem was, how could I use a strain gauge to measure stress?
I preferred that option more than the hydraulic pump you mentioned because it is less bulky. However I might consider using the hydraulic system as well.

Is there any ready made gauges on the market, which can measure stress?

 

Of course there are force gages. They are quite common. My supermarket uses them to weigh fresh fish. The fact is, if you look under strain gages, you will find stress gages. See, for example, page 1535 of the McMaster Carr catalog.

Have you thought of hacking a simple load cell from a $10 digital scale? Again, what range of pressures/forces do you need to measure? John

John

 

The range of forces I would like to work on is from zero up to some hundreds of neutons.
My problem is that I dont want the dimensions of the gauge to be large, and therefore I don't think I can use a load cell from a digital scale.
However, do you think that I can find a load cell on the market, which suits my range of forces, and whoose dimensions are not too large?

 

This load cell is not very large and can be purchased from McMaster Carr in ranges up to 5000 newtons.

View attachment 3971

Load cells in many ranges and sizes are available. To narrow your search, you need to be more definite on size, range, resolution, price, etc. John