Sensor-Tech thermometers and their probes are permanently connected together using a compression fitting. They cannot be separated or interchanged. Each combination of meter and probe is designed to operate for a dedicated range of tasks. By finely adjusting the meter any errors in the probe are offset in the thermometer.

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No further consideration needs to be given to the probe errors which are now incorporated into the thermometer readings and shown on the calibration certificate.

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Each thermometer is calibrated as a single system, which means the readings are unique for this combination only. Whenever a probe is replaced, the thermometer is always calibrated with the new probe.

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Calibration interval is one year.

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The calibration interval is one year which is also noted on calibration sticker. It is always good practice to have regular in-house calibration checks. Some customers will choose to do these checks every week or month depending on how critical the readings are, in some critical areas they may choose to do these tests at the start of each day. See our Interim Test below.

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Calibration is not simply a calibration

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Some thermometers are only taken out when needed. Others are constantly being used in multi-shift operations. Our thermometers are designed for this, that's why we call them 'Industrial Food Thermometers'.
When we receive thermometers back for calibration, it gives us an opportunity to make sure that they are fit for purpose. With many thousands of Sensor Tech thermometers out there on the Irish market we cannot afford to send back units that have potential problems.

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We may also use this opportunity to carry out upgrades to the electronics which may often go unnoticed by our customers, as there is no extra charge for it. If you have noticed an improvement in the accuracies on the calibration certificate, then this may be the reason for it.

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If within a month from being calibrated we receive a meter back for repair, we will repair and calibrate it, less the calibration charge, regardless of age. This only applies to Sensor Tech thermometers.

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In order to keep these meters looking like new, we will also replace the case and labels when needed. Batteries are also replaced when needed, again all of this is included in the fixed calibration cost. In examining a number of our thermometers it is often impossible to tell a 20 year old meter from a brand new meter without looking at the serial no. The first 4 digits of our serial no. starts with the year and month of manufacture so that a serial no. beginning 2201 was made in January 2022

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Water-resistant thermometers are needed throughout the food industry

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In the food industry, the one great enemy of electronics and their accuracies is water. All the thermometers used in these food preparation areas need to have their cases sealed and protected from water-ingress. When water contaminates the electronics it introduces competing circuits which can cause the readings to be unreliable, effectively making all its calibration and certification worthless.
Cooking area temperatures are the most critical and need special thermometers.

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Cooking thermometers need cases that are water-resistant to IP67 or better

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Cooking areas provide some of the toughest thermometer design challenges that are needed in the food industry. They need to be able to withstand the heat, steam and moisture and still maintain their accuracies in order to comply with the food safety standards.

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Sensor Tech thermometers are specially designed to operate in all areas of the food industry. Most importantly they have been tested for operation in the cooking areas, in fact we believe that if a design can survive the cooking area then it can work in all areas. We test them by total immersion and by gradually increasing the water temperature, we can test the pressure limits of the case. Increasing the water temperature results in a corresponding increase in the air pressure inside the case which can be used to test the integrity of the o-ring seal. Our tests show that these limits are well within the operational conditions found in these cooking areas, however there are limits, so we ask our customers not to leave the thermometers on top of these hot ovens or serve overs as these high temperatures can cause the seals to fail.

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When we get back a thermometer for calibration/repair, we always check it for water-ingress. The most obvious signs of water damage is condensation inside the display window. Although this is quite rare, it can be caused by heat damage. These are visible faults that the operator is aware of, however there is also the risk of water contamination that is much less noticeable, caused by the longterm effects of high humidity and high heat. With no obvious signs of moisture damage the operator is lured into a false sense that the accuracy is being maintained.

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The best way to test for this water damage is to do a regular 'Interim Calibration Test'.

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Confidence through Calibration

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From time to time we receive a call from a customer asking about the accuracy of our thermometers and wishing to return their thermometer and have it tested. As the conversation develops it becomes clear that there has been a loss of confidence in the accuracy.

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Perhaps they have tried using a boiling kettle to test for 100°C (not very accurate as the boiling point varies with atmospheric pressure and altitude, with possible errors of a degree or more, ask any jam maker?).

Perhaps they are using a dry block calibrator (rarely accurate when the pockets are not a close fit)

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Perhaps they have put two probes in the same product and found a difference in the readings (again not recommended),

Even a number of accurate thermometers laid out on a bench can give different readings. Tip; Tie the probe ends together using an elastic band and watch the readings converge.

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Perhaps they are using an oversized drill bit (6mm or 1⁄4 inch) to test frozen product and getting a high reading. Tip; Push TWO probes into the same hole which will improve thermal contact with the product and give more accurate readings.

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There are any number of these indicators that can trip up our thinking, causing a sort of cognitive dissonance to set in and challenge our core beliefs. In a busy production environment this is very understandable, we have all been there at some time, even the seasoned operator can get caught out.

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“These readings cant be right, there must be something wrong with the thermometer”

 

There have been occasions when we have gone out to investigate an issue and fallen into the same

trap which means that we now, always bring our own freshly tested thermometers with us.

To our caller, we explain that we are always happy to check out the thermometer, but before returning it for testing, we ask them to do the 'Interim Calibration Test' below and come back to us if there is still an issue. In nearly all cases this solves the problem. Whenever the accuracy is called into question, there is a need to go back to basics and find a reference point that you can believe in. This is just such a test.

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The Interim Calibration Test.
This is the most important temperature test in the food industry

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It is important to have in place a means of carrying out the 'Interim Calibration Test'. See PDF document available to download at the top of this page.

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Throughout our operational guide this is one test we will come back to, many times. Its importance cannot be overemphasized. It does not need any expensive equipment, in fact it is often the use of this high tech equipment that highlights the need for the basic simplicity and accuracy of this test.

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We recommend this test to all our customers as part of their regular in-house thermometer calibration. It is one thing to read the accuracy specification on a calibration certificate and yet quite another to have direct experience of doing this test yourself.

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It's the difference between just accepting the figures quoted on the certificate to be true and that of knowing them to be true.

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In practice any of our steel probed thermometers are accurate and stable enough to act as a reference thermometer, however we also supply a special PT100 reference thermometer that should be set aside in an office or laboratory and dedicated for calibration purposes only.

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Armed with a confidence in the accuracy of the thermometer it is then possible, through a process of elimination to focus in and target the real issues.

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Check at 0.0 C

Use ice made from ordinary tap water.  We recommend using an ice reference for its stability, accuracy and repeatability, it is mother natures reference point as it is the triple point of water. It is the point where solid ice is melting to form water which is also evaporating. This makes it a very accurate test.

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In order to make an ice reference you need to obtain some ice cubes, put them in a plastic bag and

crush them using a suitable implement such as a mallet. Ideally pack up a vacuum flask with this finely crushed ice and then add water to a level just below below the ice. More ice than water gives a slushy-ice mix.

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This means that any probe inserted in it, is in contact with the melt water only. It is portable and can be used in the lab, on the factory floor, loading bay or taken to where ever it is needed. In a vacuum flask this mixture will last for more than a day.

 

As the ice is always melting it is a important to pour out any excess water so that the water level is always maintained about an inch below the ice.

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Always use a Reference Thermometer to check that the slushy-ice mix is reading 0.0°C. Before taking any readings it is useful to give it a quick stir with the probe to ensure that 0.0C is being maintained.

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During our calibration procedure we use the triple point of water, as the absolute reference for all our thermometers. We have equipment which gives us 0.01°C all year round. In 15 years, it has held 0.01°C +/- 0.01°C. Try getting that from a reference bath or a dry block calibrator.
When you use your ice reference you are able to compare your readings to our reference thermometer.
By comparing readings against the 0.0 C reference readings on the calibration certificate., the actual readings at the point of calibration should be maintained +/- 0.1°C.

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It also checks that there are no faults with the instruments. In particular if there is any moisture inside the case it will show itself as an error in these readings. When we get back a thermometer for testing, it is the first test we do. If these readings are correct it is a strong indicator that all readings will be within specification

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High Temperature interim test

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To do this test you need a second thermometer or reference thermometer
This is a test above 60C and confirms that the higher temperature accuracies and therefore the linearity has been maintained. Tie the Thermometer Under Test (TUT) and the reference probes together, approximately a half inch from their tips using an elastic band. This creates a strong thermal contact between them. Using a container of hot water at a temperature between 60°C and 80°C (Pasteurization temperature) it is possible to compare these thermometers accurately.

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Water that is left to stand still, will form a temperature strata, hot on top and cold on the bottom. In order to prevent this it is important to use the probes to whisk the water and keep it agitated. The water does not need to maintain a stable temperature as it only serves to provide an equalizing conductive medium that allows us to make an accurate comparison of both probes.

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Even though the temperature may be falling we are only interested in the temperature difference and how it compares to the equivalent readings on the calibration certificate. This test is very important because it builds so much confidence in the whole procedure of taking temperatures.

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We can say that after tens of thousands of calibrations, when the 0.0°C test and the high test above have maintained their accuracy, then all the other readings will match the readings on the calibration certificate +/- 0.2°C.

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