Podcast
Questions and Answers
What is the boiling point of mercury?
What is the boiling point of mercury?
Mercury thermometers are less toxic than alcohol thermometers.
Mercury thermometers are less toxic than alcohol thermometers.
False (B)
What property makes the readability of mercury thermometers better than that of alcohol thermometers?
What property makes the readability of mercury thermometers better than that of alcohol thermometers?
Does not wet the wall of the thermometer
The bimetallic thermometer operates based on the unequal expansion of two different __________.
The bimetallic thermometer operates based on the unequal expansion of two different __________.
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Match the thermometer type with its characteristic.
Match the thermometer type with its characteristic.
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Which of the following is true about alcohol thermometers?
Which of the following is true about alcohol thermometers?
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The accuracy of bimetallic thermometers can range from ± 0.5 to 12 °C.
The accuracy of bimetallic thermometers can range from ± 0.5 to 12 °C.
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Which type of thermocouple junction provides the quickest response time?
Which type of thermocouple junction provides the quickest response time?
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Ungrounded junctions are faster than grounded junctions.
Ungrounded junctions are faster than grounded junctions.
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What is the primary advantage of using exposed junctions in thermocouples?
What is the primary advantage of using exposed junctions in thermocouples?
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The voltage output of a thermocouple is dependent only on the temperatures of the hot and cold junctions, T1 and T2, and is independent of the temperatures of the __________.
The voltage output of a thermocouple is dependent only on the temperatures of the hot and cold junctions, T1 and T2, and is independent of the temperatures of the __________.
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Match the thermocouple junction types with their characteristics:
Match the thermocouple junction types with their characteristics:
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What law allows a thermocouple calibrated at one temperature to be used with another reference temperature without an ice bath?
What law allows a thermocouple calibrated at one temperature to be used with another reference temperature without an ice bath?
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The Law of intermediate metals states that adding a third metal affects the output voltage of a thermocouple.
The Law of intermediate metals states that adding a third metal affects the output voltage of a thermocouple.
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What results in loss of signal quality in grounded junctions?
What results in loss of signal quality in grounded junctions?
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In thermocouples, the voltage $V_{13}$ produced by temperatures $T_1$ and $T_3$ is equal to $V_{12} + V_{23}$, according to the law of __________.
In thermocouples, the voltage $V_{13}$ produced by temperatures $T_1$ and $T_3$ is equal to $V_{12} + V_{23}$, according to the law of __________.
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What is typically required for the cold junction in a thermocouple setup?
What is typically required for the cold junction in a thermocouple setup?
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Cold junction compensation eliminates the need for an ice bath in all situations.
Cold junction compensation eliminates the need for an ice bath in all situations.
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What are instrumentation amplifiers primarily used for in thermocouple applications?
What are instrumentation amplifiers primarily used for in thermocouple applications?
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The standard specification for thermolelectric voltages is IEC _____.
The standard specification for thermolelectric voltages is IEC _____.
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Match the thermocouple classes with their descriptions:
Match the thermocouple classes with their descriptions:
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Which of the following is a benefit of using electronic cold junction compensation?
Which of the following is a benefit of using electronic cold junction compensation?
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The law of intermediate temperatures can be applied in situations where cold junction compensation is not used.
The law of intermediate temperatures can be applied in situations where cold junction compensation is not used.
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Name one standard that pertains to thermocouple cables.
Name one standard that pertains to thermocouple cables.
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Instrumentation amplifiers are characterized by their high __________ and single ended output.
Instrumentation amplifiers are characterized by their high __________ and single ended output.
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What is the recommended method to achieve accurate cold junction temperature measurement?
What is the recommended method to achieve accurate cold junction temperature measurement?
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What is the main disadvantage of using RTDs compared to thermocouples?
What is the main disadvantage of using RTDs compared to thermocouples?
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Thermistors are generally more sensitive to temperature changes than RTDs.
Thermistors are generally more sensitive to temperature changes than RTDs.
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What is the typical resistance value for most commonly used RTDs?
What is the typical resistance value for most commonly used RTDs?
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RTDs have a wide operating range from _____ °C to _____ °C.
RTDs have a wide operating range from _____ °C to _____ °C.
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Match the following temperature measurement devices with their characteristics:
Match the following temperature measurement devices with their characteristics:
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What is the output voltage from a type S thermocouple placed in an oven with an ice bath reference junction?
What is the output voltage from a type S thermocouple placed in an oven with an ice bath reference junction?
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Thermocouples can measure temperatures from -200°C to +2500°C.
Thermocouples can measure temperatures from -200°C to +2500°C.
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What are the two main types of junctions used in thermocouples?
What are the two main types of junctions used in thermocouples?
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The voltage reading from a thermocouple is affected by the temperature of the ______ junction.
The voltage reading from a thermocouple is affected by the temperature of the ______ junction.
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What is one of the limitations of thermocouples?
What is one of the limitations of thermocouples?
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Thermocouples have a risk of self-heating.
Thermocouples have a risk of self-heating.
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What output voltage would a thermocouple read if ambient air (20°C) is used for the reference instead of an ice bath?
What output voltage would a thermocouple read if ambient air (20°C) is used for the reference instead of an ice bath?
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Thermocouples are considered _______ devices since they do not require self-heating.
Thermocouples are considered _______ devices since they do not require self-heating.
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Match the following characteristics of thermocouples with their descriptions:
Match the following characteristics of thermocouples with their descriptions:
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What is a key advantage of thermocouples compared to other temperature sensors?
What is a key advantage of thermocouples compared to other temperature sensors?
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Study Notes
Temperature Measurement Techniques
- Various methods exist for measuring temperature, each with unique advantages and limitations
- Different types of sensors are used, depending on the specific application
Changes in Physical Dimensions
- Liquid-in-glass thermometers: Use the expansion of liquids, typically mercury or alcohol, within a glass tube calibrated to measure temperature. Inexpensive, simple and portable.
- Bi-metallic thermometers: Two different metals with varying thermal expansion coefficients are bonded together. The difference in their expansion/contraction creates a bending effect, used in devices like thermostats. Low-cost and stable
- Constant-volume gas thermometers: A gas-filled bulb, connected to a pressure gauge, accurate over a wide range of temperatures. More intricate compared to other types
- Infrared pyrometers: Measure the amount of infrared radiation emitted by objects.
Changes in Electrical Properties
- Thermocouples: two dissimilar metals form an electrical junction. The voltage generated is proportional to the difference between the temperatures of the hot and cold junctions (highly nonlinear, need amplification and compensation).
- Resistance Temperature Detectors (RTDs): Use the change in resistance of a metal (platinum) in response to temperature changes. They are highly accurate, stable, have high reliability, but can be complicated, bulky.
- Thermistors: Semiconductor-based devices exhibiting a high degree of nonlinearity in resistance vs temperature. Useful in applications like electronic temperature sensors due to their characteristics.
- Integrated Circuit (IC) Transistors and Diodes: Specialized ICs designed with components sensitive to temperature, providing temperature-sensing capabilities. Often used for temperature measurements, though they generally have a more limited range than the other methods.
Bimetallic Thermometers
- Range: -65 to 430°C
- Accuracy: ±0.5 to 12°C
- Advantages: Low cost and stable operation
- Disadvantages: Mechanical response time
Constant-Volume Gas Thermometers
- Pressure is linked to temperature
- Accuracy and range depend on fluid
- Low cost
- Stable in operation
Signal Conditioning in Thermocouples
- Low output voltage
- Low sensitivity, need amplification
- Non-linear output
- Need cold junction compensation
- Analog signal needs Analog-to-digital conversion
Signal Conditioning in RTDs
- Change in resistance is measured
- Uses a Wheatstone bridge for measurements
- Requires Bridge excitation to induce change in voltage
Signal Conditioning in Thermistors
- Change in resistance is measured
- Use a Wheatstone bridge
- Non-linear output
- Needs amplification and linearization
Temperature Integrated Circuits
- Semiconductor-based temperature sensors in integrated circuits
- Output is linearly proportional to absolute temperature (needs voltage supply)
- Use is limited in temperature range (-55 to +150°C)
- More versatile signal, but with smaller temperature range
Standards for Thermocouples
- IEC 60584-1: Basic values of thermoelectric voltages
- IEC 60584-2: Tolerance values of thermoelectric voltages
- IEC 60584-3: Thermocouple cables and compensating cables
- ASTM E230: Standard specification and temperature-electromotive force (EMF) tables for standardised thermocouples
- ASTM E2846-20: Standard Guide for Thermocouple Verification
Thermocouple Amplification of Signals
- Instrumentation Amplifiers are used for high-gain
- Used to amplify very small differential signals from strain gauges or thermocouples
- High-input impedance and single-ended output
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Description
Test your knowledge on the principles of temperature measurement, including the characteristics of mercury and alcohol thermometers, as well as the functioning of bimetallic and thermocouple types. This quiz will cover boiling points, accuracy, and response times of different thermometer types.
