DT-670 Silicon Diode Interfacing to a microcontroller

michael
New Member

Posts: 2

DT-670 Silicon Diode Interfacing to a microcontroller Apr 5, 2023 8:27:26 GMT -5

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Post by michael on Apr 5, 2023 8:27:26 GMT -5

We are planning to use a silicon diode temperature sensor(rather than Pt100 RTD for increased ruggedness) from Lakeshore to monitor the internal temperature of a cryogenic vacuum insulated tank.
The temperature range is between 22K to 360K.We are planning to use a CU or CY package to mount the sensor on the tank liner(aluminum) and use it to estimate the internal temperature since it should be at a similar temperature.

We plan to use the 4 wire quad twist phosphor bronze cabling with heat sinking and thermal anchoring as recommended inside the vacuum shell and then normal cabling after the vacuum port to an microcontroller for temperature measurement.

1) Interfacing to the controller : I can connect the voltage output to ADC pins. How is 10 microamps constant sensor excitation typically generated? Does it require an external precision current source ? How are these sensors typically interfaced to microcontrollers?

2) Since a transmitter is not included along with the sensor, what is typically the maximum possible length from the sensor to microcontroller?

3) How can I add a digital fieldbus protocol like RS232, RS 485 or CAN ( not Profibus) to ensure transmission to a longer distance? Is there a silicon diode transmitter available in the lakeshore catalogue?

I would like your comments on this subject and apologies for the dumb questions as I am not a cryogenic expert

.
Thanks

Lake Shore Jeff M
Lake Shore

Posts: 327

DT-670 Silicon Diode Interfacing to a microcontroller Apr 6, 2023 9:22:53 GMT -5

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Post by Lake Shore Jeff M on Apr 6, 2023 9:22:53 GMT -5

In order for the diode to work, it requires a constant 10µA excitation current be applied on the I+ & I- leads in order to read the voltage on the V+ & V- leads.

1. If you have a Lake Shore controller, the current source and voltage measurement circuits are built into the controller, otherwise, you would need to provide the 10µA current from a different device. We offer a Model 121 Current source that would work, The Inputs on any Lake Shore controllers use the 4-wire connection for the sensor.

2. The maximum length between the controller and sensor is not a fixed distance as many factors determine how far away it can be. I suggest you read the application note that was written for our Model 240 Module which offers information on the best practice for long cable lengths. www.lakeshore.com/docs/default-source/default-document-library/model240note2016.pdf?sfvrsn=8cf63d0c_3

3. We no longer offer transmitter cards, so the only option would be to use a controller or monitor that can offer RS232 interface where you can set up an application to query the temperature. We also offer an ethernet interface on our Model 224-12 Monitor or the Model 336 Temperature controller.

If you wish to discuss this in more detail, you can contact us at 614-891-2243 and select Option 2 for support or bu sending an email to support@lakeshore.com.

michael
New Member

Posts: 2

DT-670 Silicon Diode Interfacing to a microcontroller Apr 11, 2023 5:20:03 GMT -5

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Post by michael on Apr 11, 2023 5:20:03 GMT -5

Hello Jeff,
Thanks for the reply.
Unfortunately, this is not a benchtop application but an embedded automotive application, so we cannot use off the shelf current source and/or a controller/monitor.
Do I need for example something like an off the shelf LM334 from TI, in addition to generate this 10µA excitation current typically?
Do you have any application notes for interfacing these diodes to microcontrollers?
I would ideally like to avoid additional interfacing or daughter boards but if there is no other option then I may go back to RTD solution.

Lake Shore Jeff M
Lake Shore

Posts: 327

DT-670 Silicon Diode Interfacing to a microcontroller Apr 12, 2023 9:22:28 GMT -5

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Post by Lake Shore Jeff M on Apr 12, 2023 9:22:28 GMT -5

I am not familiar with the TI module you mention so I cannot answer that question.

We do not have an application note regarding using our sensors with microcontrollers and as I mentioned before, the sensor requires a 10µA excitation current in order for it to work so you may not have a choice other than a daughter card. Since the RTD sensor also requires an excitation current that you need to source the diode would ne no different other that the 10µA versus 1mA requirement for operation.