Term
| State the three basic functions of temperatures detectors. |
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Definition
| Indication alarm and control |
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Term
| Describe the two alternate methods of determining temperature when the normal temperature sensing devices are inoperable. |
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Definition
| Installed spair, contact pyrometer, external bridge |
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Term
| State the two environmental concerns that can affect the accuracy and reliability of temperature detection instrumentation |
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Definition
| Ambient temperature changes and humidity |
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Term
| Explain the basic theory of operation of a bimetallic strip thermometer |
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Definition
| Two strips of metal with different coefficients of thermal expansion are connected. Since they are connected they are always at the same temperature. Thus when heated, the strips will bend. |
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Term
Describe the basic construction of a thermocouple including: Major component arrangement Materials used |
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Definition
A thermocouple is constructed by joining two dissimilar metal wires at one end. The other end of each wire is connected to a measuring instrument. Magnesium Oxide surrounds dissimilar metals usually Platinum and another metal. It is inclosed in a thermal sheath. |
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Term
Explain how RTD resistance varies for the following: Increase in temperature Decrease in temperature |
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Definition
| An increase in temperature results in an increase of resistance. |
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Term
| Explain how a thermocouple provides an output represenative of the measured temperature. |
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Definition
Heating the measuring junction of the thermocouple produces a voltage, which is greater than the voltage across the reference junction. The difference between the two voltages is proportional to the difference in temperature and can be measured on the voltmeter (in millivolts). |
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Term
Describe the construction of a basic RTD including: Major component arrangement Materials used |
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Definition
RTD elements are usually long, spring-like wires surrounded by an insulator and enclosed in a metal sheath. RTD elements are normally constructed of platinum, copper, or nickel. |
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Term
| Explain how an RTD provides an output representative of the measured temperature. |
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Definition
A change in temperature will cause an RTD to heat or cool, producing a proportional change in resistance. A precision device that is calibrated to give the proper temperature reading measures the change in resistance. |
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Term
Given a simplified schematic diagram of a basic bridge circuit, state the purpose of the following components: R1, R2, RX, Adjustable Resistor, and Sensitive Ammeter |
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Definition
(R1 and R2) are used for ratioing the adjustable and known resistances (R3) is used to match the unknown variable resistor (Rx) is used to measure temperature A sensing ammeter indicates the current flow through the bridge circuit |
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Term
| Describe the bridge circuit conditions that create a balanced bridge |
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Definition
| The bridge circuit is considered balanced when the sensing ammeter reads zero current. |
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Term
Describe the temperature instrument indications for the following circuit faults. Short Circuit Open Circuit |
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Definition
A very high temperature indicates an open circuit in a temperature instrument. A very low temperature indicates a short circuit in a temperature instrument. |
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Term
| Explain the three methods of bridge circuit compensation for changes in ambient temperature. |
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Definition
| · Measuring circuit resistor selection · Electronic circuitry design · Use of three or four wire RTD circuits |
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Term
| Describe the two basic types of measurement. |
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Definition
Direct parameter measurement - always local measurement, measured by observing actual parameter Indirect parameter measurement - used to provide remote indication, measured by observing a physical property to determine the actual parameter. |
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Term
| Draw and label a block diagram of a basic instrument channel. |
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Definition
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Term
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Definition
| the area between the limits within which a quantity in measured |
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Term
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Definition
| The mathematical difference between the upper and lower range values. |
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Term
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Definition
"Elevated Zero Range" is a range in which the zero value of the measured variable is greater than the lower range value. |
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Term
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Definition
| "Suppressed Zero Range" is a range is which the zero value of the measured variable is less than the lower range limit |
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Term
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Definition
| the degree to which the output of an instrument approaches an accepted standard or true value. |
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