Precision Thermistor Research Articles

Robust temperature coefficient of resistance of polycrystalline La0.6Ca0.4MnO3 under magnetic fields at room temperature

In the presence of magnetic field, reducing the loss in temperature coefficient of resistance (TCR) and increasing metal−insulator transition point (TMI) to room temperature are the most important concerns for the application of perovskite manganites in high−precision thermistors. Based on emerging evidence, relevant factor to address these problems lies in the interaction between Jahn−Teller (JT) distortion and magnetic field, which results in spin−orbital coupling (SOC) effect and significantly influences TCR and TMI. In this work, we studied the magnetic field induced SOC effect in polycrystalline La1−xCaxMnO3 (x = 0.225–0.45) materials synthesized via sol−gel technique. Compounds undergo the JT distortions with increasing Ca dopant content, and the most pronounced distortion of 0.0144 at x = 0.40 is correlated with a basal−plane distortion mode. All samples exhibit TMI values between 262 K and 288 K, indicating the enhancement of doping−induced double−exchange interaction. In the magnetic field of 1 T, SOC effect sufficiently suppresses the deterioration of TCR caused by deficient magnetization in La0.6Ca0.4MnO3 to a value of 2.9%·K−1 at room temperature (287 K).

FruiTemp: Design, Implementation and Analysis for an Open-Source Temperature Logger Applied to Fruit Fly Host Experimentation

FruiTemp is an open-source prototype developed to study the response of endophytic insect species such as fruit flies (Diptera: Tephrtidae) to variable temperature conditions including the controlled laboratory and fluctuating field settings. The system is a three-channel temperature sensor that consists of two precision thermistors that measure the temperature in the core and the surface of a fruit on a tree and a Harsh Environment thermistor that measures the air temperature surrounding the host at a rate of one measurement per 15 min. The sample rate can be adjusted according to the researcher’s needs. The system was successfully tested in field and laboratory experimental conditions using apples as the fruit model. The measurements on apples on trees lasted five consecutive days and produced a range of reliable data. After assessing statistical agreement and precision, the results revealed a differential bias of 0.331 °C and a proportional bias of a magnitude of 0.982. This work promotes open-source implementations allowing inexpensive solutions aiding experimentation procedures by significantly lowering operating costs.

An on-skin platform for wireless monitoring of flow rate, cumulative loss and temperature of sweat in real time

Monitoring the flow rate, cumulative loss and temperature of sweat can provide valuable physiological insights for the diagnosis of thermoregulatory disorders and illnesses related to heat stress. However, obtaining accurate, continuous estimates of these parameters with high temporal resolution remains challenging. Here, we report a platform that can wirelessly measure sweat rate, sweat loss and skin temperature in real time. The approach combines a short, straight fluid passage to capture sweat as it emerges from the skin with a flow sensor that is based on a thermal actuator and precision thermistors, and that is physically isolated from, but thermally coupled to, the sweat. The platform transfers data autonomously using a Bluetooth Low Energy system on a chip. Our approach can also be integrated with advanced microfluidic systems and colorimetric chemical reagents for the measurement of pH and the concentration of chloride, creatinine and glucose in sweat. A wearable platform, which uses a thermal sensing module isolated from biofluids and a Bluetooth Low Energy system on a chip for wireless data transfer, can be used to continuously monitor sweat.

An accurate calorimeter-based method for the thermal characterization of heat pipes

This study presents a method that can be used to accurately determine the thermal performance of a cylindrical heat pipe. In the method, the heat pipe is placed between two stainless steel 304 cylindrical blocks, configured as radial calorimeters that achieve thermal contact with the evaporator and condenser sections of the pipe. A flexible isothermal electrical heater mat surrounds the evaporator block, and a liquid-cooled copper pipe wrapped around the condenser block is used to remove heat. High precision thermistors (±0.01 K) positioned at fixed radial locations within the calorimeters are used to measure the heat supplied to the evaporator and the heat extracted from the condenser. One-dimensional radial conduction is assumed to occur within each calorimeter, and this enables the quantification of heat flows from the temperature readings. This assumption is verified by a steady-state analysis of the radial, axial and circumferential temperature differences within the evaporator calorimeter, based on data recorded for the lowest and highest heat inputs. Furthermore, a numerical model is used to confirm that end effects have a negligible influence on radial conduction within each calorimeter. This study concludes that the most commonly used characterization techniques for heat pipes can greatly overestimate thermal performance (15–32% for input powers of 7.5–25 W respectively) due to inaccurate quantification of heat flows into the evaporator and from the condenser. The calorimetric technique reported here achieves uncertainties in thermal resistance of <7.5% for low thermal loads (<12.5 W) and <6% for higher loads (>12.5 W). Moreover, the method achieves a significant improvement in the experimental thermal efficiency, with values of >75% recorded for all heat inputs in this study. The use of radial calorimeters in the current study obviates the requirement for calculating the losses from the heater to ambient, hence achieving low uncertainties in thermal resistance and effective thermal conductivity for a range of heat inputs.

An infrared image based methodology for breast lesions screening

The objective of this paper is to evaluate the potential of utilizing a structured methodology for breast lesions screening, based on infrared imaging temperature measurements of a healthy control group to establish expected normality ranges, and of breast cancer patients, previously diagnosed through biopsies of the affected regions. An analysis of the systematic error of the infrared camera skin temperature measurements was conducted in several different regions of the body, by direct comparison to high precision thermistor temperature measurements, showing that infrared camera temperatures are consistently around 2°C above the thermistor temperatures. Therefore, a method of conjugated gradients is proposed to eliminate the infrared camera direct temperature measurement imprecision, by calculating the temperature difference between two points to cancel out the error. The method takes into account the human body approximate bilateral symmetry, and compares measured dimensionless temperature difference values (Δθ¯) between two symmetric regions of the patient’s breast, that takes into account the breast region, the surrounding ambient and the individual core temperatures, and doing so, the results interpretation for different individuals become simple and non subjective. The range of normal whole breast average dimensionless temperature differences for 101 healthy individuals was determined, and admitting that the breasts temperatures exhibit a unimodal normal distribution, the healthy normal range for each region was considered to be the dimensionless temperature difference plus/minus twice the standard deviation of the measurements, Δθ¯‾+2σΔθ¯‾, in order to represent 95% of the population. Forty-seven patients with previously diagnosed breast cancer through biopsies were examined with the method, which was capable of detecting breast abnormalities in 45 cases (96%). Therefore, the conjugated gradients method was considered effective in breast lesions screening through infrared imaging in order to recommend a biopsy, even with the use of a low optical resolution camera (160×120 pixels) and a thermal resolution of 0.1°C, whose results were compared to the results of a higher resolution camera (320×240 pixels). The main conclusion is that the results demonstrate that the method has potential for utilization as a noninvasive screening exam for individuals with breast complaints, indicating whether the patient should be submitted to a biopsy or not.

Niphargus: A silicon band-gap sensor temperature logger for high-precision environmental monitoring

A temperature logger, named “Niphargus”, was developed at the Geological Survey of Belgium to monitor temperature of local natural processes. It has a sensitivity of the order of a few hundredths of degrees on temperature variability in open air, caves, soils and river environment. The newly developed instrument uses a state-of-the-art band-gap silicon temperature sensor with integrated digital output. This sensor reduces the risk of drift associated with thermistor-based sensing devices, especially in humid environments. The Niphargus is designed to be highly reliable, low-cost and powered by a single lithium cell with up to several years autonomy, depending on the sampling rate and environmental conditions. A batch of Niphargus loggers was also compared to a precision thermistor to assess absolute temperature accuracy. Further characterization came from two field case studies in Belgium: monitoring of a mineralized water stream near the town of Spa and air temperature monitoring inside Han-sur-Lesse cave.

A Chopper Current-Feedback Instrumentation Amplifier With a 1 mHz &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$1/f$&lt;/tex&gt; &lt;/formula&gt; Noise Corner and an AC-Coupled Ripple Reduction Loop

This paper presents a chopper instrumentation amplifier for interfacing precision thermistor bridges. For high CMRR and DC gain, the amplifier employs a three-stage current-feedback topology with nested-Miller compensation. By chopping both the input and intermediate stages of the amplifier, a 1 mHz 1/f noise corner was achieved at an input-referred noise power spectral density (PSD) of 15 nV/?Hz. To reduce chopper ripple, the amplifier employs a continuous-time AC-coupled ripple reduction loop. Due to its continuous-time nature, the loop causes no noise folding to DC and hence offers improved noise performance over auto-zeroed amplifiers. The loop reduces chopper ripple by more than 60 dB, to levels below the amplifier's own input-referred noise. Furthermore, a maximum input referred offset of 5 ? V and a CMRR greater than 120 dB were measured at a supply current of 230 ?A at 5 V.

Focus on test and measurement

Focus on test and measurement

Derivation of total diffuse attenuation coefficient from water column temperature data and meteorological water surface fluxes: A simple management tool

The total diffuse attenuation coefficient of Photosynthetically Available Radiation (Kd (PAR)) is derived by optimising the solution of a surface layer model to match temperature profiles measured with a precision thermistor chain; a non‐linear least‐squares Levenberg‐Marquardt scheme is applied to optimize Kd (PAR). The method was validated in Lake Kinneret (Israel) over 10 days in summer to early winter 2001, Valle de Bravo Reservoir (Mexico) on 1 July 2004 and Winam Gulf (Kenya) on 1 May and 12 August 2005. The method was applied for cases where the horizontal pressure gradient in the surface layer was negligible, the photic depth was deeper than the diurnal surface layer and the increment in temperature in photic region was considerably larger than the thermistor's precision. In all these tests, the errors of the estimated values of Kd (PAR) were mostly within 10% of the actual direct measurements. Investigations of the sensitivity of the model revealed that the accuracy of the method depended primarily on the precision and accuracy of the thermistors as well as the vertical resolution of the temperature measurements in the surface layer; all of these determine the rate of convergence of the optimisation scheme.

THE EFFECT OF 24 HOUR COLD APPLICATION ON INTRAARTICULAR TEMPERATURE AFTER SHOULDER ARTHOSCOPY

1869 Cryotherapy is a widely used treatment method in the postoperative period, in order to have its therapeutic effects, cryotherapy needs to penetrate in the deeper tissues. The PURPOSE of this study is to examine the effect of 24 hour superficial cryotherapy application on the subacromial temperature after shoulder arthroscopy. METHODS: Fifteen patients were randomly assigned to an experimental (n=10) and control group (n=5). After shoulder arthroscopy a thermistor was left in the subacromial space, and cryotherapy was started. Cryotherapy (7°C) was applied in cycles of two hours followed by one hour during which no cryotherapy was applied, total application time was at least 15 hours, total measuring time was 24 hours. Skin temperature was measured by a Testoterm precision thermistor. A Visual Analog scale (VAS) was used to register the patients pain, a "Constant Score" was used to evaluate the functionality of the shoulder. Differences were examined with a T-test. RESULTS: As expected skin temperature differed significantly (p<0.05), subacromial temperature differed significantly 4 hours after starting measurements until T12. Maximal decrease in subacromial temperature was 4.5°C, whereas in the control group subacromial temperature increased. Other parameters also differed between groups. CONCLUSION: a decrease in subacromial temperature is only possible when cold is applied in a continues manner over a period of at least 2hours, and the subcutaneous fat tissue will also this temperature drop.

Measurement of weak absorption in optical thin films

An adiabatic laser calorimeter for measuring weak absorption in optical thin films is presented. It consists of three main parts which are used to control and measure temperature, and for calibration. The controlling temperature part is a set of automatic temperature controls mainly composed of a PID adjuster. The temperature difference between specimen and environment is always less than +/-0.006 degrees C during the measurement process. There is almost no energy exchange between specimen and environment. The specimen temperature increment is measured by a high precision thermistor set. Its measuring temperature sensitivity is 0.003 degrees C and the accuracy is +/-0.004 degrees C. The absolute electrical calibration part is used to obtain absorptance of a specimen immediately without needing to know the mass and specific heat of the specimen. Absorptance as small as 1 x10(-5) can be detected when a 1.5-W argon-ion laser is used.

An Artificial Apple Bud for Frost Temperature Sensing

ABSTRACT AN artificial apple bud was developed to replace insertion of thermocouples into real apple buds for temperature monitoring. The energy balance of an apple flower bud in the first pink stage was analyzed to determine which bud properties affect the bud-environment heat exchange. Dry and wet bud energy balances were considered. The parameters involved in the bud energy exchange were shape, emissivity, diameter, volume, density, and specific heat. Polystyrene, a plastic with thermal properties similar to an apple bud was tooled to the size and shape of a natural bud. A 3000 ohm, 1% precision thermistor was prepared and inserted into the polystryene. Ten buds were fabricated and tested. On a sample frost night, under nonsprinkled conditions, there was no difference between artificial and natural bud temperature means at a 95% confidence level two out of seven periods. The difference between the means was equal to or less than 0.8 C at all seven periods. Under sprinkled conditions, there was no difference between temperature means of any period.

Central body temperature as a guide to optimal heart rate.

Studies in man suggest that fixed-rate artificial pacemakers do not return hemodynamic function to normal, since the principal mechanism for the increase in cardiac output with exercise, increased heart rate, is not restored. Special pacemakers are available that can detect atrial activity and pace the ventricles in coordination, but nearly half of the patients receiving artificial pacemakers have abnormal atrial function (atrial fibrillation, sick sinus syndrome). This study examined the effects of exercise on the temperature of blood returning to the right atrium. Precision thermistors, placed in the right hearts of conscious dogs, recorded temperature increases of 1 degree C (range 0.4-1.5 degrees C) during submaximal treadmill exercise. Temperature change correlated well with work load and changes in heart rate.

Thermistor controlled water/oil bath for precision measurements in the range 0-30 degrees C

Mechanical and electrical details, together with performance tests, are presented for a double container 0.032 m3 thermostat for use in the temperature range 0-30 degrees C. The control system uses a precision thermistor to give a stability of <or=+or-4 mK over a period of 14 days. The short-term stability over several hours was better than +or-1.5 mK, the limit of the temperature measuring system used during tests.

A new enclosure for 54 standard cells with 25-μK stability

Ten enclosures, each capable of containing 54 standard cells have been designed and constructed. Each enclosure consists of three concentric aluminum cubes separated by foamed polystyrene insulation. The second cube only is controlled at a temperature of 22°C by a precision thermistor and an ac transformer-ratio bridge followed by a phase-sensitive detector, a dc amplifier and a heater. The drift in temperature from the initial settings over a period of 10 months has been less than 300 μK whilst the gradient across the innermost cube has not exceeded 20 μK.

Novel Precision Thermistor from Intrinsic Germanium

A precision resistive temperature sensor for the region -30° to +180° C is described. This thermistor of intrinsic single crystalline germanium features small size (even miniaturization), very short response time, low capacitance and inherent narrow tolerances in characteristic resistance and temperature sensitivity (tracking). The latter features are due to the precise definition of intrinsic conductivity together with special electrode systems which, by concentrating the field, render the outer dimensions of the thermistor chip ineffective.

A Low-Noise Thermistor Bridge for Use in Calorimetry

Abstract A precision thermistor bridge and thermistor is described for use in a thermal titration calorimeter or a high-speed stopped- or continuous-flow calorimeter of the Roughton type. These are compared and evaluated with regard to several other types of detectors, including the platinum resistance thermometer, thermocouple, transistor thermometer, and capacitance thermometers. At this time the best detection for our purpose seems to be a specially constructed 20-100 kΩ thermistor used in conjunction with a new ac lock-in amplifier bridge. The sensitivity of the system is equivalent to a peak-to-peak noise of 25 x 10-6 °C, with a 100-ms time constant and 1 µW power dissipation in the thermistor. Long-term drift of the bridge, without an oven, was 1 x 10-6 °C/min.

A coaxial millivoltmeter/milliwattmeter for frequencies up to 1 Gc/s

A description is given of a 50Ω coaxial millivoltmeter/milliwattmeter for the measurement of signal-generator output levels up to about 1 Gc/s in terms of equivalent source e.m.f. or equivalent available power. The instrument consists of a measuring head and an indicator unit. It is fully portable and requires no power supply. The measuring head comprises a precision 50Ω coaxial line terminated in a tractorially mounted resistor. The voltage across the resistor is measured by a pair of coaxial silicon diodes in a voltage-doubler circuit which minimizes the effect of source harmonics. The admittance of the diodes is compensated over the complete frequency range so that the voltage-standing-wave ratio (v.s.w.r.) is not less than 0.995. The inlet connector has a v.s.w.r. of not less than 0.999. The indicator unit contains the d.c. circuits for measuring the rectified output of the diodes and embodies an indicating instrument with a direct-reading linear power scale together with a number of resistors for calibration and temperature correction.Reference is made to the effect of ambient temperature on the sensitivity and excitation/response law of silicon diodes. A description is given of an electro-mechanical circuit, operated by a single control calibrated in terms of temperature, which not only corrects the sensitivity but also maintains a linear power response over a range of 20°C. The accuracy of the correction is such that the residual errors due to ambient temperature are not greater than 0.1%.The instrument is calibrated at 1 Mc/s by means of a special calibrator which is referred to d.c. standards. This has an inaccuracy of 0.25% on voltage at 1 Mc/s. Results are given of a comparison with a precision thermistor mount up to 1 Gc/s. These show that inaccuracies of 0.5% on voltage and 1.5% on power are not exceeded below about 800 Mc/s.

The steady‐state temperature difference in the Hill‐Baldes technique

AbstractThe molal steady‐state temperature differences δ for a number of solvents have been determined by the Hill‐Baldes technique, using a precision thermistor bridge. The values of δ obtained in the present investigation as well as those available in the literature have been explained on the basis of the theory of evaporation of droplets after introducing a thermal efficiency factor, which is characteristic of the experimental method employed. The application of this technique for the determination of molecular weights in solution is also discussed.

The steady‐state temperature difference in the Hill‐Baldes technique

AbstractThe molal steady‐state temperature differences δ for a number of solvents have been determined by the Hill‐Baldes technique, using a precision thermistor bridge. The values of δ obtained in the present investigation as well as those available in the literature have been explained on the basis of the theory of evaporation of droplets after introducing a thermal efficiency factor, which is characteristic of the experimental method employed. The application of this technique for the determination of molecular weights in solution is also discussed.