How to use one circuit to excite 5 Pt100

[loopin3]

I have a problem with excite 5 PT100. I read a more thread of read temperature with PT100 and i'm confused. My problem is how to connect 5 PT100 with multiplxer for reading one temperature in one step in a cycle of read.
First problem is how excite the RTD and second how to use, one cirucit for excite, for 5 RTD.

can you help me??

tank you.. for help.

Added after 23 minutes:

my pt100 have a two wire...

 

[FvM]

cd4051 pt100

The problem is to prevent analog multiplexer resistance from distorting the measurement. A circuit I used in several previous designs has two analog multiplexers (e. g. CD4051), one for source and one or sense. The source multiplexer is driven by a current source (reference voltage + OP + transistor) and the sense multiplexer is connected to voltage measurement. All Pt sensors have one terminal connected to ground, the other to the multilexers.

 

[laktronics]

Re: 5 Pt100

Hi,
How about using the RTDs in the feedback path of an opamp, ofcourse you will need one opamp per channel, but the advantage is the signal will be available at low impedance for subsequent use by any standard multi input ADCs as available with many new micro controllers. A common refence can be used in this case for all five channels.

Regards,
Laktronics

 

[FvM]

Re: 5 Pt100

One issue with Pt100 is, that you have to limit the operating current to a few mA to limit temperature error. This typically is handled by either using an AD with low voltage input or an amplifier. Basically, a Pt100 measurement doesn't need a stable reference, as long as it's identical with the AD reference. A low noise analog supply is usually sufficient.

But accuracy requirements for Pt100 acquisition may be different, also the existing hardware prerequisites.