Abstract
A zero-drift, mid–wave infrared (MWIR) thermometer constructed using a chopper stabilised operational amplifier (op-amp) was compared against an identical thermometer that utilised a precision op-amp. The chopper stabilised op-amp resulted in a zero-drift infrared radiation thermometer (IRT) with approximately 75% lower offset voltage, 50% lower voltage noise and less susceptibility to perturbation by external sources. This was in comparison to the precision op-amp IRT when blanked by a cover at ambient temperature. Significantly, the zero-drift IRT demonstrated improved linearity for the measurement of target temperatures between 20 °C and 70 °C compared to the precision IRT. This eases the IRT calibration procedure, leading to improvement in the tolerance of the temperature measurement of such low target temperatures. The zero-drift IRT was demonstrated to measure a target temperature of 40 °C with a reduction in the root mean square (RMS) noise from 5 K to 1 K compared to the precision IRT.
Highlights
Non-contact temperature measurements, acquired from processes using infrared radiation thermometers (IRTs), afford advantages over contact temperature measurements
These measurements were performed with (a) the IRTs blanked withaacover coverat the blackbody blackbody source source radiating radiating at atan anarbitrary arbitrary atambient ambienttemperature temperatureand and(b)
The results have demonstrated that the use of a chopper stabilised op-amp within the transimpedance amplifier (TIA) circuit of a zero-drift IRT improves the quality of the temperature measurement for target objects at ambient room temperature and above
Summary
Non-contact temperature measurements, acquired from processes using infrared radiation thermometers (IRTs), afford advantages over contact temperature measurements. These include amelioration of the susceptibility of thermocouple wires to degradation from exposure to the measurement conditions and the effects of contact upon the measurand and object [1,2]. Cooling a photon detector increases the cost and size of IRTs, making their usage undesirable, within size-constrained instrumentation [4]. Thermal detectors, such as thermopiles, can measure over this spectral range, they suffer from slow response time and low sensitivity compared to photon detectors [1]. Thermal detectors require high gain amplification to achieve output voltages that can be measured with benchtop instrumentation and can only represent, accurately, signals that change slowly, as demonstrated by Moisello et al [5]
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