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, 2024
- ASHARE Online Bookstore
- Addenda
- Errata
- ANSI/ASHRAE Standard 41.1-2024 [Go to Page]
- Contents
- Foreword
- 1. Purpose
- 2. Scope [Go to Page]
- 2.1 This standard applies to temperature measurements under laboratory and field conditions for use in performance testing heating, ventilating, air-conditioning, and refrigeration systems and components.
- 2.2 This standard does not apply to wet-bulb and dew-point temperature measurement methods within the scope of ANSI/ASHRAE Standard 41.6.
- 3. Definitions
- 4. Classifications [Go to Page]
- 4.1 Temperature and Temperature Difference Measurement Conditions. Temperature and temperature difference measurement test conditions that are within the scope of this standard shall be classified as one of the types described in Sections 4.1.1 and 4...
- 4.2 Temperature Measurement Methods. Temperature measurement methods that are within the scope of this standard are listed in Table 4-1.
- 5. Requirements [Go to Page]
- 5.1 Test Plan. The test plan shall be one of the following options:
- 5.2 Values to Be Determined and Reported. The values that are specified in the test plan in Section 5.1 shall be determined and recorded. Unless otherwise specified in the test plan, temperature measurements, temperature difference measurements, temp...
- 5.3 Test Requirements
- 6. Instruments [Go to Page]
- 6.1 Instrumentation Requirements for All Measurements
- 7. Temperature Measurement Methods [Go to Page]
- 7.1 Liquid-In-Glass Thermometers. A liquid-in-glass thermometer is a direct-reading thermometer that consists of a sealed glass enclosure that is partially filled with a liquid with a reservoir, called a “sensing bulb,” on one end. Immersing the ...
- 7.2 Thermocouples. A thermocouple consists of two wires made of different metals that are joined at one end, and that end is positioned where temperature is to be measured. The other end is electrically connected to an object, called a reference junc...
- 7.3 Resistance Temperature Detectors. Resistance temperature detectors (RTDs) are temperature sensors that contain a resistor that changes resistance value as a function of temperature changes. The metals that are used as the resistor element in RTDs...
- 7.4 Thermistors. Thermistors are temperature sensors that have a resistance that is a function of temperature. The mathematic model for thermistor temperature-resistance curves is the Steinhart-Hart equation that is provided in Equation 7-2:
- 7.5 Radiation Pyrometers. Radiation pyrometers are used to measure surface temperature without contacting the surface by detecting electromagnetic radiation emitted from a flat surface in the visible and infrared portions of the electromagnetic spect...
- 7.6 Solid-State Temperature Measurement Sensors. Solid-state temperature sensors use a diode or voltage reference that has an established voltage versus temperature characteristic together with signal-processing electronics to generate a voltage or c...
- 7.7 Bimetal Thermometers. If two strips of metal A and B with different thermal expansion coefficients αA and αB but at the same temperature are bonded together, a temperature change causes different expansion, and the strip, if unrestrained, will ...
- 7.8 Pressure Thermometers. Pressure thermometers consist of a sensitive bulb, an interconnecting capillary tube, and a pressure-measuring device that include Bourdon tubes, bellows gages, and diaphragm gages as shown schematically in Figure 7-2.4
- 7.9 Method for Measuring the Temperature Rise in Motor Windings. This section describes a method for measuring the average temperature of the windings in a copper AC or DC motor by measuring electric resistance.
- 8. Uncertainty Requirements [Go to Page]
- 8.1 Post-Test Uncertainty Analysis. A post-test analysis of the measurement system uncertainty, performed in accordance with ASME PTC 19.1 1, shall accompany each temperature and temperature difference measurement if specified in the test plan in Sec...
- 8.2 Method to Express Uncertainty. All assumptions, parameters, and calculations used in estimating uncertainty shall be clearly documented prior to expressing any uncertainty values. Uncertainty shall be expressed as shown in Equation 8-1:
- 9. Test Report [Go to Page]
- 9.1 Test Identification
- 9.2 Unit Under Test Description
- 9.3 Instrument Description
- 9.4 Measurement System Description
- 9.5 Test Conditions
- 9.6 Test Results if Required by the Test Plan in Section 5.1
- 10. References
- Informative Appendix A: Informative References and Bibliography
- Informative Appendix B: Example of an Uncertainty Estimate for a Temperature Measurement with an RTD [Go to Page]
- B1. Derive the Uncertainty Equation
- B2. Compute the Uncertainty for Application 1 [Go to Page]
- B2.1 Evaluation at =100 ohm at 0°C in SI Units
- B2.2 Evaluation at =100 ohm at 32°F in I-P Units
- B2.3 Evaluation at =113.7375 ohm at 35°C in SI Units
- B2.4 Evaluation at =113.7375 ohm at 95°F in I-P Units
- B3. Compute the Uncertainty for Application 2 [Go to Page]
- B3.1 Evaluation at =100 ohm at 0°C in SI Units
- B3.2 Evaluation at =100 ohm at 32°F in I-P Units
- B3.3 Evaluation at =113.7375 ohm at 35°C in SI Units
- B3.4 Evaluation at =113.7375 ohm at 95°C in I-P Units
- Informative Appendix C: Supplemental Information Regarding Temperature Measurement Methods [Go to Page]
- C1. Liquid-in-Glass Thermometers [Go to Page]
- C1.1 The liquid-in-glass thermometer is a direct-reading temperature instrument. It should be so placed that its indication measures the temperature at the location intended, while at the same time it should be accessible for reading. Typical accurac...
- C1.2 Precautions are necessary to ensure that heat from the body of the reader, an electric lamp, or other extraneous sources does not affect the reading.
- C1.3 Glass thermometers should not be inserted directly into a conduit conveying fluid unless calibration corrections are applied to compensate for pressure effects. For such measurements, the thermometer should be inserted into a thermometer well in...
- C1.4 Glass thermometers require correction for depth of immersion and for the temperature of the ambient around the stem. This is the emergent stem correction.
- C1.5 Glass thermometers require correction for orientation. For example, a glass thermometer inserted upside down in an air duct reads high by as much as 0.05°C (0.10°F).
- C1.6 Glass thermometers are comparatively simple to interchange between two positions for alternate readings in order to obtain an average temperature difference reading that is unaffected by the calibration of the thermometers.
- C1.7 Liquid-in-glass thermometers should not be used for transient temperature measurements.
- C2. Thermocouples [Go to Page]
- C2.1 Thermocouple Operating Principle. In 1821, a German physicist named J.T. Seebeck took two dissimilar metals, with one at a higher temperature than the other, and constructed a series-type electrical circuit by joining the two dissimilar metals t...
- C2.2 Thermocouple Laws. There are five empirical fundamental laws for thermocouple circuits:
- C2.3 Basic Thermocouple Circuit. Thermocouples are connected to measuring instruments directly or using thermocouple extension wires. Figure C-6 shows a basic thermocouple circuit that includes extension wires. This circuit includes a reference junct...
- C2.4 Wire Splices. Best practice is to not splice thermocouple wires between the measuring junction and the reference junctions.
- C2.5 Switches. If switches are used to alternately connect thermocouples to the reference junction, there should be no dissimilar metals in switching circuits unless isothermal conversion junctions are used to eliminate spurious thermocouple junction...
- C2.6 Series Thermocouple Circuits—Thermopiles. Multiple thermocouples are connected in series to increase the measurement sensitivity, because the measured emf is the sum of the individual thermocouple emfs. Figure C-7 shows multiple thermocouples ...
- C2.7 Parallel Thermocouple Circuits. Figure C-8 shows multiple thermocouples connected in parallel and connected to a common reference junction. This arrangement is often used to measure the average temperature at a single sensing location.
- C2.8 Thermocouples Used for Temperature Measurements. Thermocouples used for temperature measurements in heating, ventilating, air-conditioning, and refrigeration include, but are not limited to, the types described in Table C-1.4
- C2.9 Thermocouple Measuring Junction Configurations. The types of thermocouple measuring junction configurations shown in Figure C-9 are described in Sections C2.9.1 through C2.9.3.
- C2.10 Best Practice Thermocouple Installation Guidelines
- C2.11 Potential Thermocouple Errors
- C3. Resistance Temperature Devices (RTDs) [Go to Page]
- C3.1 The platinum RTD is used by NIST to define the International Temperature Standard (ITS-90). Platinum is often used in RTDs because of its high melting point, which allows manufacturing of high purity, better than 99.999%. Platinum has excellent ...
- C3.2 Platinum RTDs have a positive temperature coefficient and are standard in two resistance temperature coefficients: 0.00385 and 0.003925 ohm/ohm-C. The “385” coefficient is more commonly used by manufacturers. Connections to RTD elements incl...
- C3.3 Platinum RTD elements are typically manufactured for 100 ohms at 0°C (32°F). Other standard resistances include 200, 500, and 1000 ohms. Thin film platinum elements are commonly manufactured for 1000 ohm at 0°C (32°F) and are used for small-...
- C3.4 RTD probes include sheath materials of 316 stainless steel and Inconel®. Diameters range from 0.5 mm (0.020 in.) to 9.5 mm (0.375 in.) and lengths from 25.4 mm to 500 mm (1 in. to 20 in.). Response times or time constants define the time requir...
- C3.5 RTDs require an electronic instrument, recorder, indicator, meter, or data logger to derive temperature. The instrument should be calibrated for the RTD type, configuration, and coefficient, and the error should be used to determine the uncertai...
- C3.6 Platinum RTD temperature measurement range is –200°C to 3000°C (–328°F to 1112°F). Accuracy of wire-wound platinum RTDs range from 0.005°C to 0.30°C (0.01°F to 0.55°F) depending on manufacturing technique. Best accuracies are stated ...
- C3.7 Resistance temperature device bridge circuits include the three shown in Figure C-10.
- C4. Thermistors [Go to Page]
- C4.1 Thermistors, or thermally sensitive resistors, are manufactured from ceramic oxide semiconductors. Different from RTDs, thermistors have a negative thermal coefficient. Metals for precision thermometry include metal oxides of manganese, nickel, ...
- C4.2 Thermistors are fabricated in the form of beads, rods, and disks in sizes as small as 0.13 mm (0.005 in.) and are not stable until aged for multiple months. The elements are sintered integral with lead wires, then encapsulated with various mater...
- C4.3 The high sensitivity of thermistors limits their temperature span to small ranges of about 55°C (100°F) over the temperature range of –73°C to 290°C (–100°F to 550°F). Low temperature range resistances are 2000 to 10,000 ohm, with high...
- C4.4 Manufacturers of narrow-range thermistors with matched and calibrated electronic indicating or monitoring devices provide measurement accuracies greater than or equal to ±0.002°C (±0.004°F). For interchangeability of identical span and type,...
- C4.5 An example of a thermistor circuit is shown in Figure C-11.
- C5. Radiation Pyrometers [Go to Page]
- C5.1 The radiation pyrometer uses a disappearing filament or a lens system to focus the radiation onto a detector to derive temperature. The detector may be either a photocell for specific radiation bands or a thermopile for total radiation (also cal...
- C5.2 The temperature range for radiation pyrometers is –40°C to 3300°C (–40°F to 6000°F). Devices are manufactured and calibrated for smaller ranges to provide better accuracy. Handheld units have accuracies of ±1°C (2°F). Mounted units ty...
- C6. Sources of Temperature Measurement Errors [Go to Page]
- C6.1 Sources of temperature measurement error should be addressed with regard to the sensor type, usage, location, and mounting requirements based on the test plan requirements for test plan accuracy and uncertainty.
- C6.2 Sources of measurement error include the following:
- C6.3 Thermal gradient effects from the temperature differential of the measured value and the surrounding ambient temperature should be addressed by insulating the temperature probe with an insulating material supplying not less than R4.5. [Go to Page]
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