How many 2 wire rtd's can i connect to lmp90080

Hello Mike,

            Thanks For reply.

           Actually I want to us 2-wire Rtd. Can you tell me how many 2-wire RTD's can we connect to lmp90080.

Thanks in advance

M.Vijay Kumar

Hello,

Since RLINE3 is missing from the RTD you would short VIN1 and VIN6 together.  Since each RTD requires a current source, you can connect two 2 wire RTDs to the LMP90080.

Mike

Hi Vijay,

we actually have a similar part to the LMP90080 in our portfolio that can theoretically measure up to 7 2-wire RTDs. Have a look at the ADS1148. In this device the excitation current sources (IDACs) can be routed to any of the analog inputs.
You could for example use one analog input as the negative input for all 7 RTDs and then connect each positive RTD wire to a dedicated analog input.
Attached diagram shows an example for 4 2-wire RTDs.
To measure RTD4 for example you would route IDAC1 to AIN3 and measure the voltage between AIN3 and AIN4.

However in case you want to implement some external RC filters on the inputs - which we usually recommend - this will get a little bit more challenging with that approach.
In case you would be interested in going this route we can talk about it in more detail.

Regards,

Hello,

Thanks for your replies.

              According to our project budget we have to use 4 2-wire RTD's to one lmp90080. But as per your suggestion I understands that we can't connect like that. 

             I have an idea about using a 2*4 multiplexer to 2 excitation current sources for 4 2-wire RTD inputs. will it work? 

            Kindly give me solution.

Thanks in advance

M.Vijay Kumar

Hello,

I have attached a drawing of a possible way to do this.

Mike

4034.4 2 Wire RTDs.tif

Hello,Mike

      Thanks for your reply,

     Again I want help from you. Could please suggest me a best Multiplexer for this Application.

Thanks in Advance

M.Vijay Kumar

Hi,

I have not been able to find a 4:1 analog switch, so you will need to use 3  2:1 analog switches.  Take a look at the TS3A24159 or TS5A22362.

Mike

Hi Stout,

      Is it possible to connect to 4 3-wire RTD in LMP90080.?i attached the file in which I made the connection for the 4 3-wire RTDs in LMP90080. Let me know whether that connection is possible or not.?