Need guidance in designing Display for measuring device with 4-20mA output

I need to design a display for a measuring device which outputs a 4-20mA signal.

The scaling will be 4 - 20mA = 0000-9999 readings..

The device measures in micron, and the display has to be very accurate, though decimal are not required.

Please help me in planning as what bit ADC should be used. Should I use the AVR's inbuilt Analog input or use an external converter.

I am afraid with the noise.

Please help me in planning as what bit ADC should be used.

You have already been told this in another thread. The answer is at least 14 bits. The answer will not change if you ask again, it is physics.

Should I use the AVR's inbuilt Analog input or use an external converter.

The built in A/D is not accurate enough it needs to be external - you have already been told that.

I am afraid with the noise.

So put on a pair of ear defenders so the noise will not be as loud.

Grumpy_Mike:

Please help me in planning as what bit ADC should be used.

You have already been told this in another thread. The answer is at least 14 bits. The answer will not change if you ask again, it is physics.

Should I use the AVR's inbuilt Analog input or use an external converter.

The built in A/D is not accurate enough it needs to be external - you have already been told that.

I am afraid with the noise.

So put on a pair of ear defenders so the noise will not be as loud.

No no.. Sir. Mike.. Please do not get me wrong..

The previous thread started with a different subject. I had confusion is analog bit calculation.

This thread is all about the whole project..

Could you please guide me as what type of A/D converter can be used..??

An alternative method would be to use an op-amp to give a more realistic signal level. If you could then restrict your expectations to within a smaller part of it's expected full range you could then use a more practical method to read it.

For example, if you were wanting to measure the speed of a motor vehicle, you wouldn't need the result calibrated to the nearest millimeter per second for the whole range of 0 - 50,000 miles per hour.

Do you have details of the exact sensor you are trying to read and some idea of the environment in which you'll be reading it. It does sound like you may have misunderstood it's parameters.

KenTF: Do you have details of the exact sensor you are trying to read and some idea of the environment in which you'll be reading it. It does sound like you may have misunderstood it's parameters.

I don't know what sensor it is. I asked for the minimum and maximum measurements that the instrument can take. So as an example I was said that it may be able to measure 0008 - 2000 microns which will be scaled into the 4 - 20mA range.

But if the scale of the display is 4 - 20mA = 0000 - 9999 then the readings will be wrong.

I guess I will have to keep buttons on the display so that the user can set the minimum and maximum measuring value..

If you don't know what sensor it is then how are you going to build it?

Unless of course this is your homework and you are trying to get us to do it.

You don't seem to understand very much and are attempting a project that is way outside your current skill set.

Grumpy_Mike: If you don't know what sensor it is then how are you going to build it?

The sensor is inside the instrument. I guess it uses some other communication inside the instrument. But the instrument converts it to a 4 - 20mA loop communication output to connect to the primary display.

Those who gave me information were first saying that 4 - 20mA will be scaled to 0000 - 9999 on the display, but then they are saying that the minimum and maximum measurements are programmable, and for eg. 0008 - 2000 micron. If so then the 0008 - 2000 micron should be 4-20mA.

So thats why I said that if there instrument is programmable then the display should also have an option to scale its input to its minimum to maximum value.

Unless of course this is your homework and you are trying to get us to do it.

Sir, Mike.. you are again getting me wrong.

Yes, of course this is homework. But I am not getting everyone here to do it for me. I am just writing what I am told about the instrument, so that you all can help me understand.

You don't seem to understand very much and are attempting a project that is way outside your current skill set.

Yes, I am not an expert at all. I may not succeed in this project, but I don't find any problem in attempting it. I guess this will leave me at least with some knowledge.

So I am keeping a positive view.

Hi, what is the instrument called, what was originally connected to the 20mA loop?

Tom.... :)