Need for sample and hold circuit

[microcare]

Hello ppl


Im making a temperature measuring and control system .
Im using RTD in bridge circuitary whose o/p is given to instrumentation amplifier (IA)IC .
Now im planning to use adc0804 after IA stage .
Do i require to use a sample and hold (S&H)IC in between ?
Or do i require to use ADC with built in S&H circuit ?)eg.adc10064


Plz help .
It would be also nice if u can give advatage of using S&H circuitary in above cases .
Btw im using Microcontroller further after the ADC stage

 

[ericgibbs]

Hello ppl


Im making a temperature measuring and control system .
Im using RTD in bridge circuitary whose o/p is given to instrumentation amplifier (IA)IC .
Now im planning to use adc0804 after IA stage .
Do i require to use a sample and hold (S&H)IC in between ?
Or do i require to use ADC with built in S&H circuit ?)eg.adc10064


Plz help .
It would be also nice if u can give advatage of using S&H circuitary in above cases .
Btw im using Microcontroller further after the ADC stage

Hi,
The requirement for S/H depends a lot on the rate of change of the output
of the opa signal. If its 'slow' compared to the conversion rate of the ADC then its not required.
If the signal for ADC conversion is changing faster than the ADC conversion rate you can get problems.

What sampling rates/speeds are you expecting?

If you have the choice and the budget can stand it I would choose the ADC10064 device.

 

[Nigel Goodwin]

Hello ppl


Im making a temperature measuring and control system .
Im using RTD in bridge circuitary whose o/p is given to instrumentation amplifier (IA)IC .
Now im planning to use adc0804 after IA stage .
Do i require to use a sample and hold (S&H)IC in between ?
Or do i require to use ADC with built in S&H circuit ?)eg.adc10064


Plz help .
It would be also nice if u can give advatage of using S&H circuitary in above cases .
Btw im using Microcontroller further after the ADC stage

Why not just use a micro-controller with in-built ADC, including sample and hold?.

 

[microcare]

Hi , thanks fr ur suggestions,well .. the measurment and conversion both r asynchronous . The temp will b changing continuously and i want to collect the reading say after every 5 secs or so ..

 

[ericgibbs]

Hi , thanks fr ur suggestions,well .. the measurment and conversion both r asynchronous . The temp will b changing continuously and i want to collect the reading say after every 5 secs or so ..

hi,
When you say .. the measurment and conversion both r asynchronous .
This would suggest that you take a 'reading' and sometime later you do the ADC conversion,,,
if thats the case, you need a sample and hold.

Remember, even with a sample/hold device, the hold time is finite, so do the conversion as soon as possible after the sample/hold.

To say, the tempr is changing continously isn't specfic enough to provide us with any information.
I would suggest that something like 'the maximum rate of tempr change is Cdeg /sec'..

A 5sec/sample rate is low and should not be a problem.

Hope this helps.

 

[microcare]

Thanks fo ur replies guys ...i think i better proceed with s&h ckt to b on safer side .