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Category Archives: Technical Information

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

Ceramic used in High Temperature Sensor Designs

Temperature Sensors operating above 1100°C normally use ceramic protection sheaths and insulators. The most useful ceramics for temperature sensors are Recrystalised alumina and Aluminous Porcelain.

Recrystalised Alumina Ceramic

Recrystalised Alumina is commonly called RA, Alsint ®, RUBALIT ®  , AluSIK-99 ZA ®, 

RA is the higher temperature grade, with applications up to 1700°C. The specification most usually referred to is DIN 799. A similar grade DIN 710 is now no longer readily available, but it is still seen on older thermocouple specifications sheets. DIN 799 grade is minimum 99.7% Al2O3. Some ceramic shape manufacturers claim 99.8%. My understanding is that the basic raw material before extrusion is 99.8%.… Read more

POX Temperature Sensor for Chemical Plants

Peak Sensors supplies temperature sensors to many specialised applications. POX, Partial Oxidation is a chemical plant process which uses fuel / air mixture to partially oxidise the gases into other useful products. Carbon Monoxide is the common product. The POX temperature sensor requires some novel design detail to survive the plant and to be safe should failure occur.

POX Process

This process occurs at temperatures around 1200 deg C. It is a very aggressive environment for temperature sensors. Heat, Pressure, Oxygen and Combustion products are present. A number of Probes are typically situated almost within the insulation to give them some protection. As insulation deteriates over the plant life the probes get an even tougher life.… 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

Conduction Error in Temperature Sensors

Conduction error is a common problem for small application contact temperature sensors.

Temperature sensors can be very accurate devices, however poor probe design or bad installation can easily give a system significant temperature reading errors. Conduction error is primarily caused by inadequate immersion. Heavy Industrial applications usually have good immersions, but designers of small pieces of equipment must address the problem.

Sensors usually need protection sheaths and always use signal cables. Both items will conduct heat away from a system. Probe leads and sheath will pass through a thermal gradient at some point. If the thermal gradient is close to the measuring point, then the sensor will be influenced to some degree by ambient conditions.… Read more

TC Temperature Sensors

TC is a common abbreviation for Thermocouple. A TC is made from two different wires joined in a loop. When the temperatures of the joins (Hot Junction and Cold Junction) are different a very small current flows. It the cold junction is split, and a voltmeter is placed there, it detects an EMF. When the dissimilar wire alloys are defined alloy pairs, the EMF can be used to determine the temperature difference, and thus the temperature of the hot junction.

 

Common TC Pairs

 

K Type is the most common. (NiCr v NiMgAlSi) This TC operates from -200 to + 1300°C.… Read more

Aerospace Heat Treatment Thermocouples to AMS 2750D

Aerospace Heat Treatment applications require AMS 2750D thermocouples. The key point of this standard, for sensor makers, demands that Thermocouples are calibrated by approved means and shown to be within defined limits. Individual sensors or batches of Thermocouple material can be tested. The maximum acceptable error depends on sensor use. There are strict limits on the number of uses before recalibration or replacement is required.

 

Peak Sensors often supplies Mineral Insulated Thermocouples, Rare Metal Thermocouples or Thermocouple wire batch certified. Thermocouple type R, type S and type N are the most common aerospace sensors.

 

Cost Reduction for AMS 2750D

 

To minimise Mineral Insulated Thermocouple sensor costs, Peak Sensors will have batches of wire calibrated and then from it, build sensors according to a customers requirement.… Read more

Original Equipment Temperature Sensors

Many equipment designers require temperature measurement inputs in Original Equipment they are creating. Demands for thermal control, overheat protection, temperature compensation, heater and cooler switching all require system signals.

 

Working with Original Equipment Designers.

 

Peak Sensor staff are never happier than when we are talking to a design engineer about a new application. Engineers know their product well. Peak Sensors staff know about sensors. Put the two together and great solutions can emerge.

 

Good sensor design identifies the balance between a number of conflicting parameters

 

  • Probe Cost
  • System cost
  • Robustness
  • Protection from ambient conditions
  • Speed of response
  • Process connection
  • Accuracy
  • Sensor lifetime
  • Subsequent assembly
  • Replacement

 

Peak Sensors has a long history of working with designers to create optimal solutions for original equipment.… Read more