TEMPERATURE TEMPERATURE AND RELATIVE AND RELATIVE

HUMUDITYHUMUDITYMEASUREMENT MEASUREMENT INSTRUMENTSINSTRUMENTS

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Hello, I want to show you the Hello, I want to show you the various instruments we use at various instruments we use at Fresh or Freezing to measure Fresh or Freezing to measure temperature and relative temperature and relative humidity and talk about how humidity and talk about how we maintain and test them.we maintain and test them.

We use different instruments We use different instruments to measure temperature and to measure temperature and relative humidity.relative humidity.

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This is a dial thermometer.This is a dial thermometer.

This is a glass stem This is a glass stem thermometer. thermometer.

These are electronic solid state These are electronic solid state thermometers.thermometers.

Your workplace may use some or all of Your workplace may use some or all of these.these.

Let’s look at thermometers first.Let’s look at thermometers first.

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For a thermometer to be For a thermometer to be of use it must be of use it must be accurate. There are two accurate. There are two ways to test a ways to test a thermometer for thermometer for accuracy:accuracy:

An ice and water An ice and water mixmix

(O (O CC) and compare ) and compare your readings.your readings.

Steam (100 Steam (100 C) and C) and compare your compare your readings.readings.

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This is an ice and water This is an ice and water test. test. We normally work We normally work on systems that are on systems that are close to 0 °C. So it is close to 0 °C. So it is more sensible to use the more sensible to use the ice and water method to ice and water method to check/calibrate check/calibrate thermometers.thermometers.

Be very careful when Be very careful when testing as both methods testing as both methods are dangerous – you can are dangerous – you can get cold burns as well as get cold burns as well as hot burns. hot burns.

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When taking readings, be When taking readings, be careful. You will be working on an careful. You will be working on an operating unit. You need to be operating unit. You need to be aware of rotating machinery, as aware of rotating machinery, as well as the fact that some well as the fact that some components will be very hot or components will be very hot or cold.cold.

The techniques and sometimes The techniques and sometimes the locations for taking the locations for taking temperatures will vary from temperatures will vary from thermometer to thermometer.thermometer to thermometer. You need to be careful to ensure that you make sure You need to be careful to ensure that you make sure

the sensing element or bulb is actually in contact the sensing element or bulb is actually in contact with the component whose temperature you are with the component whose temperature you are trying to measure.trying to measure.

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There are There are a few points to a few points to remember about measuring remember about measuring relative humidity. To measure relative humidity. To measure relative humidity both wet relative humidity both wet bulb and dry bulb bulb and dry bulb thermometers are needed. thermometers are needed. Usually both types of Usually both types of thermometers are mounted in thermometers are mounted in a frame with the wet bulb a frame with the wet bulb thermometer covered with a thermometer covered with a wet wick.wet wick. A device mounted in a common frame is called a A device mounted in a common frame is called a

sling psychrometer. These are available in a sling psychrometer. These are available in a number of styles using either normal bulb type number of styles using either normal bulb type thermometers or a digital type thermometer.thermometers or a digital type thermometer.

Take care to only use distilled water for wetting Take care to only use distilled water for wetting the wick as non-distilled water will give incorrect the wick as non-distilled water will give incorrect readings because of impurities in the water.readings because of impurities in the water.© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence

Sling psychrometers are usually Sling psychrometers are usually rotated at approximately two to rotated at approximately two to three times per second. But three times per second. But check the instructions for each check the instructions for each sling psychrometer, just to sling psychrometer, just to make sure of the rotation rate make sure of the rotation rate required.required.

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This is a digital This is a digital psychrometer. psychrometer.

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MostMost of the instruments are of the instruments are fragile so we need to store fragile so we need to store and maintain them properly and maintain them properly so they give us accurate so they give us accurate readings. I always make sure readings. I always make sure they are clean and placed in they are clean and placed in their correct storage place their correct storage place when I’ve finished using when I’ve finished using them.them.

Cleaning normally means Cleaning normally means cleaning the sensing bulb of cleaning the sensing bulb of the thermometer. This helps the thermometer. This helps control contamination control contamination between products as well as between products as well as providing accurate readings.providing accurate readings.

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