Hi,

I am a biomedical engineering grad student. In our lab we are using edwards pressure transducers (TruWave) for various purposes. Since we are a couple of students sharing only one box I looked into making one myself.

I have taken my last circuit class a couple of years ago, so be patient with me .

This morning I have read through old threads and postings regarding this topic and got some information out of it. However, it did not really give me a definite solution.

What I think I need:

- A voltage source for the semiconductor wheatstone bridge (Voltage unknown, I am assuming it will be between 5 and 10 volts)
- an instrumentation amplifier with a gain of around 1000 (here comes a question into play, single or dual source?)
- depending on the choice of the in-amp a single or dual voltage source
- an ac-dc converter

I have looked a numerous in-amps (analog devices AD620 etc.). However, all the specs showed a very simplistic picture of bridge amplification circuits. Is it really that simple?

Would it be cheaper to buy a AC-DC to 10V converter and use a voltage divider to a achieve the +/- 5V I need for the in-amp or would it make more sense to buy a AC-DC +/- 5V converter?

Would be great if you guys could give me your input on that!

Thanks a lot.

Manuel

 

Hello,

Take a look in the attached PDF on bridge circuits.

Greetings,
Bertus

 

Hi,

thanks for your response. However, I might be wrong but I don't feel that my answers got answered completely. The article mainly discusses the advantage of ACDs for bridge conditioning. I'd like to read the signals as analog signals between -10 and 10 Volts.

Any suggestions for the questions asked in the original thread?

Thanks,

Manuel

 

What I think I need:

- A voltage source for the semiconductor wheatstone bridge (Voltage unknown, I am assuming it will be between 5 and 10 volts)

You need to define your requirements a bit more here.

- an instrumentation amplifier with a gain of around 1000 (here comes a question into play, single or dual source?)

Read through this instrumentation amplifier application note from Intersil:
http://www.intersil.com/data/an/an1298.pdf

Then have a look at the INA128/INA129 instrumentation amplifiers from Texas Instruments/BurrBrown just for comparison:
http://www.ociw.edu/instrumentation/ccd/parts/INA128.pdf

- depending on the choice of the in-amp a single or dual voltage source

The amplifier you choose and your requirements will steer you towards the appropriate supply to use.

- an ac-dc converter

For low noise, you'll probably want a linear supply rather than a switching supply.

Would it be cheaper to buy a AC-DC to 10V converter and use a voltage divider to a achieve the +/- 5V I need for the in-amp or would it make more sense to buy a AC-DC +/- 5V converter?

We have no clue where you live, so don't know what you might obtain at a reasonable cost.

 

You need to define your requirements a bit more here.

Hey, the problem is, I don't really know what voltage I'll need. The specs define the excitation impedance as 350 Ohms. How do I determine the voltage I need?

Then have a look at the INA128/INA129 instrumentation amplifiers from Texas Instruments/BurrBrown just for comparison:
http://www.ociw.edu/instrumentation/ccd/parts/INA128.pdf

I took a look at copied a diagram that was given in the pdf. Is it going to be that primitive?

The amplifier you choose and your requirements will steer you towards the appropriate supply to use.

Well, this exaclty is my problem. I am trying to find out what requirements I have? The question is, in case I use a single source supply, I guess there is no way I'll get negative values for Vout, right? Since I need negative readings I guess I have to go for a dual supply?

For low noise, you'll probably want a linear supply rather than a switching supply.

What kind of supplies or sources am I exactly looking for? It is desireably to keep it low cost.

Thanks a lot.

Manuel