ASHRAE Standard 41.1 2020

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ASHRAE Standard 41.1-2020 — Standard Methods for Temperature Measurement (ANSI Approved)

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ASHRAE	2020	30

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Description

ASHRAE Standard 41.1 prescribes methods for measuring temperature under laboratory and field conditions for use in testing heating, ventilating, air-conditioning, and refrigeration systems and components.The following changes are new in the 2020 edition:- Added new method to determine steady-state test criteria.- Updated Informative Appendix B, Examples of Uncertainty Estimates.- Much of Section 7, “Temperature Test Methods,” to the 2013 edition, has been moved to Informative Appendix C, “Supplemental Information Regarding Temperature Measurement Methods.”

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PDF Pages	PDF Title
1	ANSI/ASHRAE Standard 41.1-2020
3	CONTENTS
4	FOREWORD 1. PURPOSE 2. SCOPE 3. DEFINITIONS 4. CLASSIFICATIONS 4.1 Temperature Measurement Methods. Temperature measurement methods that are within the scope of this standard are listed in Table 4-1. 4.2 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 in Sections 4.2.1 or 4.2.2.
5	5. REQUIREMENTS 5.1 Test Plan. A test plan shall specify the temperature measurement system accuracy and the test points to be performed. The test plan shall be one of the following documents: 5.2 Values to be Determined and Reported. The test values to be determined and reported shall be as shown in Table 5-1. Use the units of measure in Table 5-1 unless otherwise specified in the test plan in Section 5.1. 5.3 Accuracy. A selected temperature or temperature difference measurement system accuracy shall meet or exceed the required temperature measurement system accuracy specified in the test plan in Section 5.1 over the full range of operating conditions. 5.4 Uncertainty. The uncertainty in each temperature and temperature difference measurement shall be estimated as described in Section 10 for each test point. Alternatively, the worst- case uncertainty for all test points shall be estimated and repor… 5.5 Steady-State Test Criteria. Temperature and temperature difference test data shall be recorded at steady-state conditions unless otherwise specified in the test plan in Section 5.1. If the test plan requires temperature or temperature difference …
11	5.6 Unsteady Temperature Measurements. If required by the test plan in Section 5.1, temperature and temperature difference test data shall be recorded 5.7 Thermowells. A thermowell consists of a tube closed at one end that is chemically compatible with the selected sensor materials. ASME PTC 19.3 TW-2017 1 provides descriptions and application specifics for thermowells. Thermowells shall be used in… 6. INSTRUMENTS 6.1 Instrumentation Requirements for All Measurements 7. TEMPERATURE MEASUREMENT METHODS 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 j…
12	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…
13	7.7 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 ANALYSIS 8.1 Uncertainty Estimate. An estimate of the measurement system uncertainty, performed in accordance with ASME PTC 19.1 5, shall accompany each temperature measurement. Where two temperature measuring instruments are used to measure a temperature dif… 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:
14	9. TEST REPORT 9.1 Test Identification 9.2 Test Conditions 9.3 Unit Under Test Description 9.4 Measurement System Description 9.5 Test Results 10. REFERENCES
15	INFORMATIVE APPENDIX A: INFORMATIVE REFERENCES AND BIBLIOGRAPHY
16	INFORMATIVE APPENDIX B: EXAMPLE OF AN UNCERTAINTY ESTIMATE FOR A TEMPERATURE MEASUREMENT WITH AN RTD B1. DERIVE THE UNCERTAINTY EQUATION B2. COMPUTE THE UNCERTAINTY FOR APPLICATION 1 B2.1 Evaluation at = 100 ohm at 0°C
17	B2.2 Evaluation at = 100 ohm at 32°F B2.3 Evaluation at = 113.7375 ohm at 35°C
18	B2.4 Evaluation at = 113.7375 ohm at 95°F B3. COMPUTE THE UNCERTAINTY FOR APPLICATION 2 B3.1 Evaluation at = 100 ohm at 0°C B3.2 Evaluation at = 100 ohm at 32°F
19	B3.3 Evaluation at = 113.7375 ohm at 35°C B3.4 Evaluation at = 113.7375 ohm at 95°F
20	INFORMATIVE APPENDIX C: SUPPLEMENTAL INFORMATION REGARDING TEMPERATURE MEASUREMENT METHODS C1. LIQUID-IN-GLASS THERMOMETERS 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 from 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 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:
21	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.
22	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 that are described in Table C-1 5. C2.9 Thermocouple Measuring Junction Configurations. The types of thermocouple measuring junction configurations shown in Figure C-9 are as detailed in Sections C2.9.1 through C2.9.3.
24	C2.10 Best Practice Thermocouple Installation Guidelines C2.11 Potential Thermocouple Errors C3. RESISTANCE TEMPERATURE DEVICES (RTDs) 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…
25	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 i… C3.3 Platinum RTD elements are typically manufactured for 100 ohms at 0°C (32°F). Other standards 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. Diameters range from 0.5 mm (0.020 in.) to 9.5 mm (3/8 in.) and lengths from 25.4 to 500 mm (1 in. to 20 in.). Response times or time constants define the time required for a 63% change… 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 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 materi… 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.
26	C5. RADIATION PYROMETERS 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…
27	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 C6.1 Sources of temperature measurement error should be addressed with regard to the sensor type, use, 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.

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Standard Title	ASHRAE Standard 41.1-2020 — Standard Methods for Temperature Measurement (ANSI Approved)
Published Code	ASHRAE
Publication Date	2020
Pages Count	30

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ASHRAE Standard 41.1 2020

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