Element and Assembly Resistance Thermometer Accuracy

Resistance Thermometer, Pt 100, RTD, whatever you call them, are devices that change resistance with temperature. They are available in a number of defined accuracy bands.

European Resistance Thermometers are usually available as 100Ω at 0°C and 138.5Ω at 100°C according to BS EN 60751 with a linear resistance change within and beyond these temperatures. Resistance Thermometers can be set to 500 or 1000 Ω

Elements can be rated to -200°C and up to +600°C.

RTD’s can be more accurate than Thermocouples, however the expected accuracy of an assembly can easily be misunderstood.

Common Resistance Thermometer Element Types

The Pt 100 sensing element is available in a number of forms:

Thin Film elements are the volume leader inexpensive device.… Read more

High Voltage Temperature Sensor Design

Temperature sensors regularly go into some very unpleasant environments. Usually this involves chemicals, pressure, temperature extremes or high vibration. Recently we had an enquiry for Resistance Thermometers (Pt 100) to go into high voltage transformers. The probe specification included a test at 3600V AC for 1 minute. Peak Sensors had very little experience of a high voltage temperature sensor.

The best designs come from collaborative efforts. Peak Sensors knew all the details about making and protecting the probe. The customer was familar with high voltages.

Insulation

The usual insulating polymers (PVC, PTFE, PFA Silicon Rubber) used with temperature sensors were not good enough insulators.… Read more

Temperature Sensor Selection for Design Engineers: Technology Review

Temperature is probably the most commonly measured physical parameter. Appropriate temperature sensor selection is essential. Designers have to decide on the best technology to employ considering the design brief. The sensor design comprises the employed sensor technology and the protection of the sensor from the process. This article covers the choice of temperature sensor selection.

Temperature Sensor Selection Technology Review

Each common technology has attributes:

	Thermocouple	Thermistor	Resistance Thermometer	Digital Sensor	Infrared
Temp Range °C	-270 to +2000	-90 to + 130	-200 to + 600	-10 to +85	-50 to 3000
Cost	Medium to Very High	Low	Low	Medium	High
Instrumentation	Readily Available or designed on a board	Designed in Circuit board	Readily Available or designed on a board	Designed in Circuit board	IR Supplier
Linearity	Non Linear	NTC’s are Non Linear	Linear	Linear
Signal	mV	K Ohms	100 / 1000 Ohms	Digital
Accuracy	Fair	Fair	Good	Excellent	Fair
Extension Cable	2 leads made of TC Extension Cable	2 leads	2, 3 or 4 leads	3 Leads
Notes	Cold Junction Compensation		Lead resistance can be significant		Non Contact Optical Sensor.

Identifying Temperature Sensor Type

We often receive phone calls from potential customers who have a temperature sensor in their hands, but little other information about it. This presents us with a number of problems. The first issue is identifying exactly what type of sensor it is.

Most industrial plant contact temperature sensors are thermocouples, resistance thermometers or thermistors. To identify the type of sensor, our advice goes along the lines of:

Is there any visible information on the instrument that displays the temperature?
What temperatures are usually recorded?
How many and what colour are any wires on the sensor or subsequent cabling?
Disconnect the sensor from the system and take a resistance measurement across any terminals on the sensor with a multimeter.