LTC2983 Measuring NTC 100K

Question

Hello, 
 I would like to measure NTC 100Kohm with 2 wires. 
 how it can be implemented? 
 What is the expected error contribution. 
 Regards

ADIApproved · Accepted Answer

Hi Mike2020 , I am transferring this query to the Analog Devices EngineerZone - Temperature Sensors Q&A forum. 
 To be able to measure an NTC 100kohm with 2 wires, you need to configure the LTC2983 to measure custom thermistors. To do this, you would need either a Steinhart-hart coefficient specific to your thermistor or a table of the resistance given the temperature in Kelvin of your thermistor. 
 I would suggest exploring the LTC2983 Demo Software for the specific configuration. Please also look at the 'Custom Sensors' section of the document provided via this link . As for the expected error contribution of the LTC2983 to your measurements, it is expected to contribute a maximum of 0.1&deg;C when measuring thermistors using a 10kohm sense resistor. Please see Table 1 of the datasheet for more details. I hope this helps. Regards, Karlo)

ADIApproved · Answer

Hi Mike2020 , Here are the answers to your questions: 1. The part is thoroughly tested using a 10kOhm sense resistor, we don't recommend otherwise. 
 1.1. The voltage dropped on Rsense would actually depend on the user-selectable current excitation. You have to make sure that the differential voltage across any of your ADC inputs is within the differential input range of +-Vref/2. You can refer to the LTC2983 Demo software for the possible value of the excitation current. 
 2. Using a single shared sense resistor, it is possible to measure 9 thermistors simultaneously. Please refer to Figure 30 of the datasheet for an example of the wiring to make this possible. 
 3. Unfortunately, the LTC2983 does not have an EEPROM to store user-defined values when the power is off. It is however possible to save on the LTC2984. 
 4. The datasheet specifies a maximum error of 0.1&deg;C for thermistor measurements within the range of -40&deg;C to 85&deg;C. This is the maximum error contribution of the LTC2983 to the measurement. However, you have to take into account the errors due to inaccuracies of the thermistor itself, as well as the Steinhart-Hart coefficients given by the manufacturer of the thermistor. I would also recommend reading this Journal written by Logan Cummings for your reference: https://www.analog.com/media/en/technical-documentation/lt-journal-article/LTJournal-V27N1-00-df-LTC298x-LoganCummings.pdf . It discusses filtering strategies for better accuracy for the different types of sensors, as well as considerations when utilizing multiple sensors simultaneously. Regards, Karlo

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LTC2983 Measuring NTC 100K