Temperature circuit help

[kmillar]

I'm looking for some help designing a crcuit to measure temperature in
a central heating system.

Sepcifically, I have a ZWorld OP7200 programmable display which has
several Analog inputs.

I have no trouble writing the sofware to read the analog inputs, but
would like some help deisgning the external circuitry. What type of
temperature sensors should I use? Temperature Dependant Resistors?
Something else? There will be 2 of them in total, one recording
temperature of flow from the boiler, and one reading temperature of
water returning to the boiler, by being clamped onto the copper pipes,
near the boiler.

Any help would be gratefully accepted, schematics (JPG or Eagle etc)
would be fantastic. It doesn't need to be specific to the OP7200.

 

[j.b. miller]

When I designed remote energy management systems, I used the National
LM34DZ temperature sensor and an LM358 dual opamp. Used one stage as a
buffer the other a simple x4 amplifier.
My systems also monitored boiler emps as well. Simply use a gearclamp and
lightly hold the LM34 onto the pipe.
It's not real 'rocket science' and you will have to experiment to get the
gain right for you application.Nice thing about the LM34, 70*F = .700 volts
!
Good luck , it is easy though

Jay

 

"kmillar" <kenny@kmillar.co.uk> wrote:

I'm looking for some help designing a crcuit to measure temperature in
a central heating system.

Sepcifically, I have a ZWorld OP7200 programmable display which has
several Analog inputs.

I have no trouble writing the sofware to read the analog inputs, but
would like some help deisgning the external circuitry. What type of
temperature sensors should I use? Temperature Dependant Resistors?
Something else? There will be 2 of them in total, one recording
temperature of flow from the boiler, and one reading temperature of
water returning to the boiler, by being clamped onto the copper pipes,
near the boiler.

Any help would be gratefully accepted, schematics (JPG or Eagle etc)
would be fantastic. It doesn't need to be specific to the OP7200.

I would side-step all the analog stuff and go directly to digital.
Maxim/Dallas has a chip that speaks 3-wire SPI and would be ideal for your
purpose,
It's their DS1626/DS1726.

Jim



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[Robert Baer]

kmillar wrote:

I'm looking for some help designing a crcuit to measure temperature in
a central heating system.

Sepcifically, I have a ZWorld OP7200 programmable display which has
several Analog inputs.

I have no trouble writing the sofware to read the analog inputs, but
would like some help deisgning the external circuitry. What type of
temperature sensors should I use? Temperature Dependant Resistors?
Something else? There will be 2 of them in total, one recording
temperature of flow from the boiler, and one reading temperature of
water returning to the boiler, by being clamped onto the copper pipes,
near the boiler.

Any help would be gratefully accepted, schematics (JPG or Eagle etc)
would be fantastic. It doesn't need to be specific to the OP7200.

I have found the LM35DT to be linear and accurate to at least 185C.

 

[Ted Edwards]

Robert Baer wrote:

kmillar wrote:
I'm looking for some help designing a crcuit to measure temperature in
a central heating system.

Is this a hot water system for your home?

temperature sensors should I use? Temperature Dependant Resistors?

Nope.

I have found the LM35DT to be linear and accurate to at least 185C.

That's the one I was thinking of. Linear, accurate and no hassles
assuming the answer to the above question is yes. If much above 100C,
then thermocouple and more complicated circuitry.

Ted

 

[kmillar]

The max output temp is 85 degrees C
It is a domestic central heating system, split into 2 zones., the CH
and the Hot water.

I wish to measure the temp of the 'flow' and 'return' close to the
boiler.
It's all part of a bigger project to autmate my home central heating so
I can monitor and control it via the web.

Thanks for all the replies. I think I have all I need now.