Resistance/Temperature Sensors & Applications
By: Donald Lupo
390765 S Wixom Road, PO Box 437
Wixom, MI 48393-7037 USA
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P 248-624-1541
F 248-624-9234
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Agenda
• Discuss Three Sensor Types
◦ Potentiometers/Slidewires
◦ Thermistors
◦ Resistance Temperature Detectors (RTD’s)
•
•
•
•
Applications
Construction
Measurement Technique
Acromag Amplifier Interface Solutions
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Potentiometer/Slidewire Sensors
• What Are They?
◦ Variable Resistance Sensors
◦ 3-Wire Terminal Resistor
▪ Two Ends and a Sliding Wiper
▪ Used as a Voltage Divider
◦ 2-Wire Terminal Resistor
▪ One end and Wiper (Rheostat)
▪ Used as a Variable Resistor
• Two Basic Types
◦ Rotary and Linear (Slider)
• Who Invented the Sensor?
◦ Johann Christian Poggendorff
(1796-1877) in 1841
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Potentiometer/Slidewire Applications
• How are they used?
◦ Manual Control of an Analog
Signals (ie; Voltage Divider)
◦ Position Adjust(ie; Gates/Valves)
◦ Position Sensing/Feedback (Servo
Controls)
◦ Speed/Motor Controls
◦ Temperature Controls
◦ Audio/Volume Controls
◦ Lighting/Dimmer Controls
◦ Circuit Gain/Bias/Attenuators
• Many Consumer/Industrial Apps
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Potentiometer Construction
• Wirewound
• Carbon
• Cermet
• Metal Film
• Conductive Plastic
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Measurement Technique
• 3-Wire Sensor (Position-Best)
◦ Stable Excitation Source
◦ Low Voltage/Power Exc
◦ Pot Value >=1000ohms for
lead wire resistance to be
negligible
▪ 20Awg, 0.01ohm/ft
◦ Pot Value as low as possible
for source impedance
purposes (ie; 10Kohm is 2500
ohms of source impedance)
◦ % of Excitation Measurement
◦ Op Temp Changes - Immune
• 2-Wire Sensor (Position-Good)
◦ Resistance Measurement
◦ Op Temp Changes - Affected
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Acromag New Solutions
Model TT234-0600
--USB Config
--Sink/Source
4-20mA Outputs
-- -40 to 80C Amb
-- CE, UL/cUL Div2
Model TT334-0700
--USB Config
--Universal V/I
Outputs
-- -40 to 80C Amb
--CE, UL/cUL Div2
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Thermistor Sensors
• What Are They?
◦ “Thermal Resistors”
◦ Variable Resistance to Temperature
◦ Low Ranges (-90 to 130C), High Res
◦ 2-Wire Connection, Fast Response
• Two Basic Types
◦ PTC – Positive Temp Coeff.
◦ NTC – Negative Temp Coeff.
• Who Invented the Sensor?
◦ Discovered 1833, Michael Faraday
▪ Silver Sulfide behavior
◦ Invented 1930, Samuel Ruben
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Thermistor Applications
• How are they used?
◦ PTC – current limiter, fuse
◦ PTC – degaussing circuits in CRT
◦ PTC – heaters
◦ NTC – PS inrush current limiter
◦ NTC – Temperature Monitoring
▪ Resistance Thermometers
▪ Incubators, 3D Printers, Batteries
▪ Automotive Coolant/Oil
▪ Engine Manifold Temps
▪ Food Industry, Processing Equip
▪ Consumer Appliances – Toasters,
Coffee Makers, Freezers, Dryers
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Thermistor Construction
• PTC
◦ Doped Polycrystalline Ceramic
▪ BaTiO3
◦ Plastic/Carbon Grains
◦ W. Heywang & G H Jonker
modeled in 1960’s
• NTC
◦ Semiconductor
▪ Pressed Disc or Cast Chip
• Steinhart-Hart Equation
1/T =A+B(ln R)+C(ln R)^3
T=Kelvins, R= Resistance
A,B,C = Steinhart-Hart parameters
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Temperature
Sensor
Comparisons
Advantages &
DisAdvantages
--Source:
Agilent
Technologies
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Measurement Technique
• 2-Wire Sensor (NTC-Temps)
◦ Voltage Divider Measurement
◦ Stable Excitation Source
◦ <=3K Thermistor Ranges, typ
▪ 0-150C (10K to 0 ohms)
▪ -40 to 150C (100K to 0 Ohms)
◦ 5K-10K Thermistor Ranges,typ
▪ 0-150C (30K to 0 ohms)
▪ -40 to 150C (240K to 0 ohms)
◦ High Ohms/C output
◦ Needs Linearization to Temp
◦ Leadwire Resistance - Neg
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Acromag New Solutions
Model TT234-0600
--USB Config
--Sink/Source
4-20mA Outputs
-- -40 to 80C Amb
--CE, UL/cUL Div2
Model TT334-0700
--USB Config
--Universal V/I
Outputs
-- -40 to 80C Amb
--CE, UL/cUL Div2
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Acromag New Solutions – Thermistor Continued
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Acromag New Solutions – Thermistor Continued
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Resistance Temperature Detector (RTD) Sensors
• What Are They?
◦ Variable Resistance Sensors
◦ Used for Temperature Measurement
◦ Uses the temperature coefficient of
base metals
• Three Basic Sensor Types
◦ Platinum (100/200/500/1000 ohm)
◦ Copper (10 ohm)
◦ Nickel (120 ohm)
• Who Invented the Sensor?
◦ Werner Von Siemens, 1871
◦ Hugh Longbourne Callendar, 1885
◦ Callendar-Van Dusen, 1925
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RTD Applications
• How are they used?
◦ Precision Temperature
Measurements
▪ Contact
▪ Non-Contact
◦ Range: -200 to +500C range
◦ Heaters, Liquids, Air Flow, MCC
◦ Motor Winding’s/Bearing Temp
◦ HVAC, Environmental Controls
◦ Sanitary/Pharm/Food/Dairy/Bev
◦ Alt. to TC’s and Thermistors
• Many Consumer/Industrial Apps
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RTD Construction
• Thin Film
• Wire-Wound
• Coiled
• Others:
◦ Carbon
◦ Strain Free
• 2,3,4-Wire Sensor Connection
◦ 2, No Lead-wire Compensation
◦ 3, Good Lead-wire Compensation
◦ 4, Best Lead-wire Compensation
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Temperature
Sensor
Comparisons
Advantages &
DisAdvantages
--Source:
Agilent
Technologies
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Measurement Technique
• 2-Wire Connection (Poor)
◦ No-lead wire compensation
◦ Keep lead wires short
◦ Can be “failsafe”
• 3-Wire Connection (Good-typ)
◦ Includes lead-wire
compensation (ie; 3rd wire
benefit)
◦ Lead wires should be balanced
◦ Can go long distances, 10ohms
per leg typical
• 4-Wire Connection (Best)
◦ Includes lead wire
compensation (2 Exc, 2Sense)
◦ Kelvin Type Connection
◦ Leads don’t need balance
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Acromag New Solutions
Model TT235-0600
--USB Config
--Sink/Source
4-20mA Outputs
-- -40 to 80C Amb
--CE, UL/cUL Div2
Model TT335-0700
--USB Config
--Universal V/I Output
(+/-10Vdc,+/-20mA,
4-20mA)
-- -40 to 80C Amb
--CE, UL/cUL Div2
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TT230 – Universal 4-20mA w/ Sink/Source Output
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TT330 – Universal Voltage/Current Output
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Summary
• Potentiometers/Slidewires
◦ Position Sensor, Resistance, Linear
▪ 3-Wire Sensed as Voltage Divider
▪ 2-Wire Sensed as Rheostat
◦ Used for Manual Control/Adjust
◦ 3-Wire Connection – Best, typical (Position)
◦ 1000ohm, 2000ohm, or <10Kohm best
• Thermistors
◦ NTC most popular for Temperature Sensing
◦ 2-Wire Sensor, Narrow Ranges: 0-100C,
◦ Low Cost, Fast Acting, but Non-Linear
• RTD’s
◦ 100ohm PT, 385 most popular
◦ Wider Temperature -200 to 500C
◦ Slow Response, High Accuracy, Stable
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Thank you!
• Questions?
• For More Information:
◦ www.acromag.com/tt
◦ Tel. 248-295-0880
◦ Email: sales@acromag.com
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