I want to generic hardware for RTD to connect both 2 wire and 3 wire types. However I should connect 4 RTDs to one IC. I want to use PT100 and PT1000 RTD types on the same configuration. What can you advise me? Should I use analog switch IC(if it's, which one?), or different connection method? Addition of that, I want to ask a question about Rsense, should I use Rsense sharing to yield max channel number and interchangeability?
Hi,
If you want to design a generic 2-wire or 3-wire sensor using the same connection port, you don’t need an external switch IC to do it. The LTC2984 input pin requirements for 2-wire and 3-wire pins are the same. See the example below. Take note that RTD and SENSE resistor channel assignment follows a general convention shown in Figure 14 in the datasheet. You just need to program the device sensor config bits B20 and B21 to determine if the RTD is a 2 or 3 wire type. To maximize the number of RTDs per LTC2984, use RSENSE sharing capability.
The example below is an interchangeable 2wire or 3wire config with shared RSENE generated from LTC298x evaluation software. You can use this to get a good idea of how to configure and program LTC298x.
The example below is a 5 sets interchangeable 2wire and 3wire configuration. Each of these sets has a separate sense resistor.
As mentioned, the RTD channel assignments follow the general convention. For example, in a 3-wire RTD application, RTD terminal1 is tied to device CHRTD (tied to Ch4 in the example provided), terminal2 to CHRTD-1 (Ch3), and terminal 3 to CHRSENSE (Ch2). The sense resistor terminals are tied between CHRSENSE (Ch2) and CHRSENSE-1 (CH1), where CHRSENSE (Ch2) is also tied to the 3rd terminal of the RTD. You need two adjacent channels to connect your RTDs terminal1 and 2. For more information, please refer to page 40 in LTC2984 datasheet.
I hope I answered your questions.
