Thermocouples, RTDs, and thermistors for industrial monitoring, scientific experiments, and reaction characterization.
Temperature of a system is an important factor that can give insight into numerous characteristics of a system. For example, in a chemical reaction, a decrease in temperature (absorption of energy) reveals that the interaction is endothermic. Conversely, if the system increases in temperature (releases heat) an exothermic reaction has occurred. One reaction studied was the interaction between pigs’ tissue and the hemostatic agent known as QuikClot. By use of a thermocouple, the temperature of the tissue was monitored when put in contact with two variations of QuikClot, one that was the traditional highly exothermic formula, and another that was a non-exothermic version of the product. Through this experiment, the data acquired by the thermocouples enabled successful evaluation of potential burn effects of the traditional QuikClot formula.1
Another useful application of temperature measurement is monitoring the stability of a mechanical system. For example, temperature measurements of an operational motor could yield data about whether the motor is working correctly. A huge spike in temperature could indicate a problem with operation, whereas a consistent temperature would correspond to a functioning system.
The most common sensors used to measure temperature are thermocouples and thermistors. Thermistors measure temperature by changes in their own resistance as the temperature of the system evolves, whereas thermocouples produce a voltage that is directly related to the temperature of the system. Thermistors are generally the more economic option of the two and also do not require any amplification of the signal they produce. Frequently, however, a wheatstone bridge is required for operation. Thermocouples on the other hand are generally more reliable and less susceptible to electrical noise. However, amplification of the thermocouple’s signal is required due to its being in the millivolt range. On any model of the Nyquist, an analog input port would be used, and through this channel the sensor could deliver data for acquisition. The sensors are generally powered by 3.3 V or 5 V, and extra circuit components such as resistors and capacitors are not usually needed for operation.
1 Arnaud, F., Tomori, T., Carr, W. et al. Ann Biomed Eng (2008) 36: 1708
2 Courtesy of Vernier
Recommended DAQ
Recommended DAQ: Nyquist 1 or Nyquist 2
Most thermocouple and RTD signals fit comfortably in the 0–5 V range and don’t require simultaneous sampling. NQ1 covers basic temperature logging; step up to NQ2 (24-bit) when you need to resolve sub-degree drift over long runs.
Code example
The DAQiFi Python SDK exposes a property-based API. Below is a minimal stream — discover the device, enable an analog-input channel, and print samples at 1 kS/s.
from daqifi import DAQiFiDevice
with DAQiFiDevice.discover_first() as dev:
dev.channels.ai0.enable()
for sample in dev.stream(rate_hz=1000):
print(sample)
For C#, Java, LabVIEW, or Node.js examples, see the open-source stack page or jump straight into the reference example app on GitHub.
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