"Speech has power. Words do not fade. What starts out as a sound, ends in a deed." -Abraham Joshua Herschel

 

PTOA Segment #111: Instrument Tech Must-Knows: Stuff That Impacts Thermocouple Measurement Accuracy

Special Limits of Error (for a Thermocouple): The phrase refers to the "intrinsic instrument measurement error" that can be expected for a thermocouple which has been manufactured with higher-quality grade thermocouple wire (as opposed to the optional "standard-grade" thermocouple wire).

The higher quality wire costs more which also makes the thermocouple "special."

The range of intrinsic instrument measurement error for a thermocouple which has been manufactured with "special grade" thermocouple wire will be significantly less compared to the measurement error range of the optional "standard grade" thermocouple.

 

Standard Limits of Error (for a Thermocouple): The phrase refers to the "intrinsic instrument measurement error" that can be expected for a thermocouple which has been manufactured with standard grade thermocouple wire (as opposed to the optional, higher-quality "special-grade" thermocouple wire).

The range of intrinsic instrument measurement error for a thermocouple that has been manufactured with "standard grade" thermocouple wire will be significantly greater compared to the measurement error range of the optional "special-grade" thermocouple.

 

 

PTOA Segment #112: Instrument Tech Must-Knows: Thermocouple Final Analysis

 

Point-Source Temperature Measurement: A unique capability of thermocouple technology to be manufactured and/or physically situated in such a way that allows a temperature measurement to be "pin-pointed" or distinguished as opposed to a temperature measurement that approximates the temperature of a much larger area (e.g. the ambient temperature of a room) or of a bulk flowing fluid.

 

 

PTOA Segment #113: Resistance . . . Is Not Futile!

(Electrical) Resistance: The amount of volts (V) divided by the amount of  Current (I) at any point in a simple electrical circuit.

Resistance is measured in ohms and the symbol for ohms is: Ω .

 

Resistance Temperature Detector (RTD): An electrical temperature detecting and measuring instrument that accurately infers a temperature because of the one-to-one correspondence between the sensed temperature and the ohms output of the RTD.

 

Resistor: An electrical circuit component that is wired into the circuit for the purpose of controlling the flow of current through the circuit.

 

Variable Resistor: An electrical circuit component that functions like a resistor except that the voltage is adjustable by a human being, ergo the output in ohms is likewise adjustable.

 

 

PTOA Segment #114: RTD-TWO

Wheatstone Bridge: An electric circuit architecture that performs two important functions related to platinum RTD output:

• Determines the unknown electrical resistance that is also the output of the Wheatstone Bridge in the (non-standard signal form) of ohms.
• Conveys the varying ohms output of the Wheatstone Bridge to an electrical circuit component that converts the non-standard electrical signal ohms output into a standard signal form that is thence transmitted to the next temperature control loop instrument.

 

 

PTOA Segment #115: Instrument Tech Must-Knows: RTD Bridge Circuits

Lead-Wire Error: A type of measurement error unique to RTDs which is caused by the two RTD lead wires naturally being impacted by ambient conditions which results in the generation of undesirable ohm output that interferes with the RTD output related to measuring a process temperature.

The amount of lead-wire error generated depends upon:

• What the wires are made of (usually copper).
• The wire diameter (aka wire gauge).
• The wire length.

Modifying the Wheatstone Bridge to accommodate 3-lead wires and 4-lead wires greatly reduces the measurement error attributable to  lead-wire error.

 

Self-Heating Resistance Interference: A type of measurement error unique to RTDs that is caused by the required DC current power supply to the RTD which generates an undesirable ohm output that interferes with the RTD output related to measuring a process temperature.

Self-Heating Resistance Interference is reduced by maintaining the DC current for just that required for circuit "excitation."

 

 

PTOA Segment #116: ALIKE … THEN AGAIN … TOTALLY DIFFERENT

NTC Thermistor: A thermistor which will exhibit a decrease in resistance output as the detected temperature increases (and vice versa).

NTC Thermistors provide the temperature monitoring technology in many consumer electronics.

 

PTC Thermistor: A thermistor which will exhibit an increase in resistance output as the detected temperature increases (and vice versa).

PTC thermistors can be used in industry for protection against excessively high temperatures and currents, for example protecting motor windings.

 

Thermistor: A temperature monitoring technology/instrument fabricated from metal oxides that generates a robust change in electrical resistance that can be correlated to a detected change in temperature.

 

 

PTOA Segment #117: Instrument Tech Must-Knows About Thermistors

Characteristic Curve (of a Thermistor): The unique curve for each type of thermistor which illustrates the resistance output expected from the thermistor at each temperature it detects.

The characteristic curve for a thermistor illustrates a predictable albeit non linear relationship between a thermistor's ohm output and the sensed temperature.

The Steinhart-Hart equation can be used by DCS software to linearize the relationship between thermistor ohm output and the sensed temperature.

 

(Thermistor) Self-Heating (Error): A type of measurement error unique to thermistors caused by ambient conditions impacting the device and which is best reduced by leaving it up to experts to determine the best service application of a thermistor.

 

 

PTOA Segment #118: No Touching!

Broadband Pyrometer: The classification of pyrometers into which infrared (IR) pyrometers fit.

 

Infrared (Spectrum of Light): The region of the Electromagnetic Spectrum from which most emitted radiation from a surface occurs and that includes the following wavelengths:

• near infrared = 0.7 - 1.3 micrometers.
• mid infrared = 1.3 - 3.0 micrometers.
• far infrared (aka thermal) wavelengths = 3.0 - 5.0 micrometers AND 8 - 14 micrometers.

 

Infrared (IR) Pyrometer: A pyrometer that can infer a surface temperature via focusing emitted radiated light in the optical and infrared spectra (aka the 0.35 µ through 14 µ wavelength range) on the measuring junction of an actual thermal element such as a thermistor, thermocouple, RTD or otherwise a photo cell.

 

Narrowband Pyrometer: The classification of pyrometers into which optical pyrometers fit.

 

Optical Pyrometer: A pyrometer that operates in the visible spectrum (.35 to .70 µ) and which compares the emitted radiation to a platinum filament to infer a surface temperature.

 

Pyrometry: A technology used to infer the temperature of a surface via the intensity of emitted radiation from that surface.

 

Visible Spectrum of Light: The small portion of the Electromagnetic Spectrum that includes 0.40 to 0.70 µ long wavelengths ... and which provide the light (and ergo colors) human beings can detect with their eyeballs.

 

 

PTOA Segment #119: Cross The Process Variable Finish Line!

PTOA Segment #119 summarized the content and applied STEM competencies PTOA Readers and Students learned while completing the PTOA Temperature Detection and Measurement Focus Study.

No additional process industry jargon appeared in this PTOA Segment.

 

PTOA Segment #120: The Method To The Madness is Revealed

PTOA Segment #120 summarized the content and applied STEM competencies PTOA Readers and Students learned while completing the entire PTOA Process Variable Temperature Focus Study Area.

The PTOA Temperature-related Focus Studies included in the PTOA Temperature Focus Study Area were:

PV TEMPERATURE FOCUS STUDY #1
INTRODUCTION TO THE PROCESS VARIABLE TEMPERATURE

PV TEMPERATURE FOCUS STUDY #2:
TEMPERATURE-CHANGING EQUIPMENT

PV TEMPERATURE FOCUS STUDY #3:
HEAT TRANSFER 

FOCUS STUDY #4:
PV TEMPERATURE DETECTION AND MEASUREMENT

No additional process industry jargon appeared in this PTOA Segment.

 

All PTOA Readers and Students who have read the PTOA Segments in the intended sequential order have totally completed the

PTOA PROCESS VARIABLE TEMPERATURE FOCUS STUDY AREA!

Bravo!

 

Next Up ...

 

THE PTOA PROCESS VARIABLE PRESSURE FOCUS STUDY AREA!

 

©2016 PTOA Segment 0137
PTOA Process Industry Jargon Recap 4-5

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