Michigan Scientific Corporation (MSC) offers a variety of thermocouple amplifier products. We strive to meet our customers’ requirements for different thermocouple types, input/output ranges, and measurement accuracy. In this first of a two-part blog series, we will start with examining why thermocouple amplifiers are necessary.
What is a thermocouple?
A thermocouple (TC) is a simple, two-wire sensor that produces a voltage proportional to the temperature difference between the measurement junction (located at the point where you are trying to sense temperature) and the cold junction (located at the measurement device or data acquisition). For a technical explanation of the physics behind thermocouple measurements, refer to Michigan Scientific’s Tech Note 102-B.
Why do I need thermocouple amplifiers?
One advantage of a TC amplifier is noise reduction. Unamplified TC signals are in the milli- or even microvolt range, and thus are susceptible to being buried in ambient electrical noise. This is especially true when running long TC sensor wires. MSC amplifiers can be located at, or very near, the measurement junction, transforming the TC signal to a high-level voltage and greatly improving the signal-to-noise ratio.
Figure 1 shows data captured from an unamplified thermocouple. The scaling is 50 mV per segment, so we can see that the peak-to-peak measurement of the noise “hash” is about 30 mV. This is a room temperature measurement, around 25°C, so the unamplified signal is about 1 mV. In this case the signal-to-noise ratio is 1/30. Keep in mind that this measurement was taken in a low-noise environment, and could be much worse.
Figure 2 shows data captured from a Michigan Scientific thermocouple amplifier. The same 25°C measurement is amplified to around 125 mV, and the noise peak-to-peak is slightly reduced to around 25 mV. This improves our signal-to-noise ratio from 1/30 to 5, a 150x improvement.
Since thermocouples only measure the temperature difference between their two junctions, a temperature measurement must be made at the cold junction and “added” to the overall measurement. All MSC thermocouple amplifiers provide cold-junction compensation and create an absolute temperature measurement.
Thermocouple sensor measurements are natively non-linear. Several MSC thermocouple amplifiers provide a linear output, reducing the need for complicated post-processing by the user.
Thermocouples with Slip Rings
The last main advantage of thermocouple amplifiers is apparent when combining TC measurements with a slip ring assembly. Slip ring assemblies do not provide connections made of thermocouple alloys, so any temperature gradient from the rotor to stator connections will not be included in the final measurement. For a more in-depth examination of this calculation, refer to Michigan Scientific’s Tech Note 102-B. By using an amplifier on the spinning side of a rotating measurement, an absolute measurement is provided that is not susceptible to temperature gradients.
Below is a video showing the effects of temperature drift while using thermocouples and a slip ring assembly and how using an amplifier impacts the output.
Stay tuned for Part Two: How to Choose the Correct Amplifier for Your Application