NT38D01 FAQ OEM ODM

Hello,
I am looking for an NTC temperature sensor-to-RS485 converter capable of measuring temperatures between at least -10°C and -30°C (preferably -40°C).
And since we plan to use various types of NTC sensors and would also like to measure with higher accuracy, we need to read the measured resistance value, which we will convert to temperature in the measurement program using the calibration parameters A, B, and C of the Steinhart-Hart equation.

I see that you offer two modules for NTC thermometers:
1) the NTA8A01, which does not return the measured resistance value and is designed only for 10k NTCs with capability to measure up to -20°C, and
2) the NT38D01, which can measure resistance but is only rated for a 5V power supply.

So I wanted to ask if it would be possible to modify, for example, the NTA8A01 module so that:
1) it could measure resistance
2) it could measure resistance up to 300 kOhm (which, even with a 10K NTC thermistor, would allow temperatures to be measured down to nearly -40°C). Or at least up to 150 kOhm (which would allow for the same capability when using a 5K NTC thermistor).

3) be supplied without pre-installed connectors.

Eletechsup: Only the NT38D01 is suitable; you can purchase the DD4012SA_5V power conversion module. Convert 12-24V voltage to DC 5V

That's exactly what I wrote: the NT38D01 module is designed only for a 5V supply voltage. And it doesn't have a place for a voltage regulator, unlike, for example, the NTA8A01 module. In our industrial conditions, we use a 15VDC supply voltage, but at the ends of the lines, it drops as low as 10VDC.

I assume that the current NTA8A01 measures resistance up to 100 kOhm. That would be sufficient for measuring temperatures down to -35°C when using a 1K NTC thermistor. The main question, then, is whether it’s possible to modify the firmware to measure resistance.
Alternatively, we could modify the resistive divider by replacing ourselves the resistor on the supplied converters.

Eletechsup :
NTA8A01 cannot meet your needs by modifying the firmware and hardware.
A new architecture is required.

And what exactly does that entail? Modifying some of the existing module? What will be the maximum resistance that can be measured? What will be the power supply range (the same as for the NTA8A01, i.e., 6–25 VDC)?

Eletechsup
1 Existing modules cannot be modified.
2 Customized version measurable range: 0.1K -300K
3 Power supply range is 6-25VDC (same as NTA8A01)

That looks good.
I’m just wondering if a development fee of $500 is really necessary? You can continue to offer the module in your online store, and you’ll be unique because no one else offers a universal resistance meter. And if you added the ability to enter the R25 and B25/85 parameters (or even the A, B, and C parameters for very precise measurements) to the firmware, it could also serve as a universal thermistor thermometer for a wide range of thermistors (5K, 10K, 50K, 100K) as well as various types of thermostors from different manufacturers (with different B constants).

And one last question: What is the accuracy of the resistance measurement? For example, you state that the NTA8A01 module, including the NTC thermistor, has an accuracy of ±1% (even though the The specified accuracy of the thermistor itself is ±1%—and is likely lower, since the accuracy of the R25 resistor itself is ±1% and the accuracy of the B constant is also ±1%. My concern is that the accuracy should be good enough. And it shouldn't be significantly lower than that of a module from another manufacturer that I have on my desk, for which the manufacturer specifies a resistance measurement accuracy of ±0.1%. Yet the actual accuracy is only around 6%.

Eletechsup: NTC is non-linear. It only has a relatively accurate value at 25 degrees Celsius.

Yes, I know. And you are not exactly right (as can be seen from the attached picture). But I am asking for resistance accuracy.

Eletechsup: Do you mean the accuracy of the resistance measurement? It is possible to achieve 1% through calibration. Our plan is as follows: 4 channels with four ranges, corresponding to 2k, 10k, 50k, and 100k NTC respectively.

1% accuracy will be acceptable.

You write "...to achieve 1% accuracy through calibration...". How will the calibration be done? By the poti? Or by adjusting some correction factor in the registry?

Eletechsup: Achieve this through the calibration register.

Eletechsup: What is the measurement temperature range? Minimum -40°C, maximum what is it?

Primarily, we measure cold chain. That means from room temperature to -30°C (or sporadically up to -40°C). Usually, we use DS18B20 thermometers. But sometimes there are freezers, where the 6 mm probe cannot be installed due to its diameter. So, in this case, we plan to use a miniature NTC probe.