# Circuit for temperature measurement ?

C

#### Chan

Jan 1, 1970
0
Hello all,
In the folowing circuit for temperature measurement

http://www.geocities.com/x_file_space/tempcct.gif

there is a sensor device. As it is not indicated what this
device is I was wondering if someone can hazard a guess
to what it could be, or suggest something that would fit
in.
Thanks

J

#### JeB

Jan 1, 1970
0
Hello all,
In the folowing circuit for temperature measurement

http://www.geocities.com/x_file_space/tempcct.gif

there is a sensor device. As it is not indicated what this
device is I was wondering if someone can hazard a guess
to what it could be, or suggest something that would fit
in.

definately "hazard"ing ... take a look a LM335.

C

#### CFoley1064

Jan 1, 1970
0
Hello all,
In the folowing circuit for temperature measurement

http://www.geocities.com/x_file_space/tempcct.gif

there is a sensor device. As it is not indicated what this
device is I was wondering if someone can hazard a guess
to what it could be, or suggest something that would fit
in.
Thanks

Hi, Chan. I think you've got an AD590 two-terminal temperature-to-current
converter, manufactured by Analog Devices. Its output is 1 microamp per degree
Kelvin, which would give you 273uA at 0 degrees C, and 373uA at 100 degrees C.
Referring to the schematic, here's the non-technical way of looking at the
circuit:

Assuming the - input of the op amp is at gnd potential, the more the temp goes
up, the more current the AD590 pulls out of the node, the more the op amp
output has to put in to keep it in balance. So, the op amp output voltage will
increase linearly as temperature rises.

The neat thing about the AD590 is that it's pretty much impervious to voltage
drops from wiring, so the sensor can be some distance from the amplifier. It
was one of the first real IC temperature sensors. The down side is that it's a
little pricey. Depending on accuracy desired, Newark sells different classes
of AD590 from $6.50 to$95.00 USD each. Intersil makes a cross for the JH
suffix only.

Good luck
Chris

C

#### Chan

Jan 1, 1970
0
JeB said:
definately "hazard"ing ... take a look a LM335.

looks like the other poster is correct as the component should
be a temperature dependent current source, whereas the
LM335 is a voltage source. But useful to have in mind all the
same.

Thanks all.

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