TDC1000: Wrong temperature results with TDC7200-TDC1000

Harry Kioleidis

Part Number: TDC1000
Other Parts Discussed in Thread: TDC7200

I am trying to measure temperature with TDC1000 and TDC7200 and one RTD. I am changing the CONFIG_2 register to 1 for temperature measurement mode and also configured the chip for a 1kΩ RTD.

The temperature measurement block works at 1 MHz from the TX_FREQ_DIV field configuration in the CONFIG_0 register.

I am getting 1 Start and 5 Stop pulses as expected but the TDC7200 returns wrong results. I am getting a result close to 2kΩ for the RTD which is unlikely.

Are there any other configurations that i neglected to address? I have tried measuring the timings (Figure 26) with the averaging of the results, as the TDC1000 and TDC7200 allow that, but have also tried without any averaging with no luck.

regards

over 6 years ago

0 Bharat Aravamudhan over 6 years ago

TI__Genius 11015 points

HArry,

I will received your question, I will check and respond to this soon.

0 Harry Kioleidis over 6 years ago in reply to Bharat Aravamudhan

Prodigy 40 points

Really need your help on this.
thanks

0 Bharat Aravamudhan over 6 years ago in reply to Harry Kioleidis

TI__Genius 11015 points

Harry,

I am working on this issue and I will get back you by this week.

0 Bharat Aravamudhan over 6 years ago in reply to Bharat Aravamudhan

TI__Genius 11015 points

Harry,

Please note if you are using the TDC1000-TDC7200EVM with the GUI:

This situation is caused by erroneous short pulses generated when measuring the resistance of the RTD. The mechanism and workaround for this behavior is described in the following application note:

Measuring an RTD Sensor with the TDC1000 and TDC7200 for Ultrasonic Sensing: www.ti.com/.../snaa230.pdf

When measuring the temperature value with the TDC1000-TDC7200 GUI ensure that the TEMP_MODE on the TDC1000 page is set to "REF_RTD1_RTD2", and that TEMP_RTD_MODE on the TEMPERATURE page is set to "RTD1 and RTD2" regardless of whether one or two RTDs are being measured at that time. The GUI automatically implements the workaround to provide the correct reading for RTD1.

0 Harry Kioleidis over 6 years ago in reply to Bharat Aravamudhan

Prodigy 40 points

I am not using the evaluation board. I made my own and the TOF measurements work great. I only have issues with temperature readings. Do i need to change measurement mode or something else?

I now realized that this issue is only present when a PT1000 is connected. If i connect a simple 990Ω resistor it measures the "temperature" but with erratic results that range from -15C to -22C.

Any ideas?

thanks

0 Bharat Aravamudhan over 6 years ago in reply to Harry Kioleidis

TI__Genius 11015 points

Harry,

You select the type of resistor in the TEMP_RTD_SEL bit & a temperature-stable external reference resistor (RREF). If the RTD type is PT500, then RREF should be 500 Ω. If the RTD type is PT1000, then RREF should be 1 kΩ. The reference resistor needs to have either a low temperature coefficient or be calibrated for temperature shift. Also are you testing the temperature in sub zero temperature? At this time we do not have any specific reason for the kind of error that you seem to see with the PT1000

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TDC1000: Wrong temperature results with TDC7200-TDC1000