​During a recent UKAS audit of an accredited calibration laboratory the assessor witnessed the calibration of an SPRT using a Triple Point of Water cell (0.01 °C).  For interest they decided to put the SPRT in an ICERO+ (0 °C) to see what the difference was.  The ICERO+ uses water with lump ice rather than crushed cubes and is stirred using air bubbling through the mixture.  The effective difference between the Triple Point value and the Icero+ value was 2 mK (0.002 °C).  Not bad for an ice bath you can use with or without mains power and can be held in one hand.  See the products tab to get more information or contact Dave Ayres:  info@benrhos.co.uk  

Answers
 

1. If a temperature controller has a set-point of 121°C, and the control sensor is a platinum resistance thermometer, whose resistance is increasing with time due to ageing;  does the process temperature increase, stay at 121°C or decrease as the PRT ages?  The process temperature decreases because as the PRT's resistance increases due to ageing the controller lowers the temperature to reduce the resistance it is used to control the temperature to the set-point.
2. If a temperature controller has a set-point of -20°C, and the control sensor is a platinum resistance thermometer, whose resistance is increasing with time due to ageing;  does the process temperature increase, stay at -20°C or decrease as the PRT ages?  The process temperature decreases as per the explanation above.

Answers next week but also consider how a temperature indicator would respond.  The indicated temperature will increase  because the PRT's resistance has increased.
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Questions
 

1. If a temperature controller has a set-point of 121°C, and the control sensor is a platinum resistance thermometer, whose resistance is increasing with time due to ageing;  does the process temperature increase, stay at 121°C or decrease as the PRT ages?
2. If a temperature controller has a set-point of -20°C, and the control sensor is a platinum resistance thermometer, whose resistance is increasing with time due to ageing;  does the process temperature increase, stay at -20°C or decrease as the PRT ages?

Answers next week but also consider how a temperature indicator would respond.
 
Some of the intriguing discussions from our temperature course for more information contact Dave Ayres at:  info@benrhos.co.uk

Our view to the questions from last week:
  

• Do thermocouples measure absolute temperature or temperature difference?  Answer: Temperature difference because the output is proportional to the temperature difference between the reference and the measuring junctions.

 

• Do resistance thermometers measure absolute temperature or temperature difference?  Answer:  Absolute temperature because the sensor's resistance is dependent on the its local average temperature.

 

• What is the temperature scale in use in the UK and is Centigrade the unit of measurement?  Answer:  The International Temperature Scale of 1990 with Celsius as the unit of measurement.

 

• Is temperature the amount of thermal energy an object has?  Answer:  Temperature is better described as the intensity of the thermal energy or the kinetic energy density.

 

• Do temperature measurements need an uncertainty associated with them? Answer: All measurements are useless without an uncertainty.

Just 5 questions to see if you need a temperature course.  Our responses next week.
  

• Do thermocouples measure absolute temperature or temperature difference?

 

• Do resistance thermometers measure absolute temperature or temperature difference?

 

• What is the temperature scale in use in the UK and is Centigrade the unit of measurement?

 

• Is temperature the amount of thermal energy an object has?

 

• Do temperature measurements need an uncertainty associated with them?

Benrhos, Rotronic Instruments  and Chamois Metrology are sponsoring this year’s British University Kayak Expedition to Russia:
​https://www.facebook.com/British-University-Kayak-Expedition-2019-330455807790207/

The images below are of our latest machined copper block for a customer’s stirred water calibration bath.  It is 250 mm long by 80 mm in diameter.  The probe holes are 10 mm in diameter and drilled to an impressive depth of 200 mm.  Drain holes 3 mm in diameter are through drilled into the probe holes to make life easier when the block is removed from the bath and needs draining.  See below for an image of the top of the block and one of the base.

How and where to measure the temperature?
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Globe gas and radiation combined temperature thermometer.
Using the combined temperature measurement from inside the ball and the gas temperature measurement from the exposed thermometer, a better idea of the temperatures personnel are experiencing can be made.
 
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The Benrhos Globe thermometer is designed to measure the combination of the temperature of gases and the effect of thermal radiation experienced by fire fighters during training and workers in a hot processing environment.  From our experience the thermometers used in live fire training facilities do not measure the true temperature on those near the fire.  This is mainly due to 4 reasons:

1. The thermometers are not immersed sufficiently into the space whose temperature is to be measured.  This results in a ‘stem error’ where the temperature on the cold side of the thermometer cools the stem of the thermometer on the hot side causing it to read low.  A rough guide for the immersion length would be 40 X diameter of the thermometer or more.
2. The thermometer is physically too large and hence slow to react to the temperature fluctuations it is subjected to.
3. The thermometer is not placed in the optimum position.
4. The thermometer mostly reads the temperature of the gases surrounding it and not the effect of the radiant heat.

It is always worth bearing in mind that, ‘a measurement is meaningless without an uncertainty associated with it’.  For example if the maximum temperature allowable in training is 250°C how close should you measure it ±1°C or ±10°C or even +1°C/--10°C?
 
The Combi thermometer is a development based on having a black ball that is about the size of parts of a human that are likely to get too hot, such as a hand or the back of the neck.  The ball is coated in a high emissivity coating so it absorbs most of the radiant heat that impinges on it.  Inside the ball is a fast response thermometer that measures the combined effect of the radiation and the local gas temperature to give a truer indication of what personnel would be experiencing.  Attached close to the ball is another fast response thermometer that measures the gas temperature.  Its job is to pick up any rapidly changing temperature such as a steam surge.  The temperatures can be displayed locally or transmitted via WiFi to remote locations.