Choose the right meters when testing for humidity.
There are a wide range of instruments used to measure Relative Humidity and Dewpoint. Old school uses Sling Psychrometers to determine these measurements while new school uses electronic meters. There are advantages and disadvantages to both. Everything being equal, to skip the conclusion of this blog, I recommend going electronic. Now, lets explore why.
Sling psychrometers vs. electronic meters
Pros of sling psychrometers: Provide wet and dry bulb measurements, are considered standard tools, can supplement other instruments, do not require batteries can be cheaper than electronic meters.
Cons of sling psychrometers: Thermometers can be hard to read, red column can separate, needs to be stored in correct temperature. At high temperatures (above 85oF) they can be highly inaccurate. (SEE: ACCURACY AND LINEARITY OF SLING AND DIGITAL PSYCHROMETERS in this Blog)
Electronic meters range from $30.00 to over $1000.00. If you buy a midrange psychrometer, while it is more expensive, it Is less prone to operator error when used properly. Some psychrometers offer a calibration kit to verify accuracy. The calibration/verification test generally takes 60 to 90 minutes. Many electronic meters have the added capability of being able to measure surface temperature via a built in thermocouple or a built in IR gun. Since ambient conditions can vary in a few feet, electronic meters make it easier to test where you are doing the work. Conditions may be good to paint on one side of a tank but not on the other side.. it's necessary to gather as much specific data as possible. Finally, the data from these sources can be ported electronically for storage and analysis. The main detriment comes when users don't maintain the tools successfully, as older models may be more prone to error.
Pros of electronic meters: Better accuracy than a sling, electronic data, time stamping for better details.
Cons of electronic meters: May cost more for better units, batteries can go dead. Lower cost unit sensors may not hold their accuracy.
Whether using a sling psychrometer or an electronic meter, it is important to let the temperature of the gauge stabilize prior to taking measurements. This can be 5 to 20 minutes for a sling or 15 to 30 minutes for an electronic meter
Choosing and preparing the right methods
Before you use an electronic meter, it's wise to check the battery. I have seen low batteries give incorrect readings on electronic meters. With sling psychrometers, users should examine the wick to make sure it's clean and white, as well as soaked with distilled or demineralized water. The thermometers should agree with each other prior to doing the sling,
It is generally best to make sure everyone on the project is on the same page when it comes to Relative / Dewpoint measurements. Slings will not always agree with electronic meters, especially in hot weather (Above 85oF). If using a sling in hot weather – make sure you use the ventilation method and not by using the sling method.
Automatic and manual calculations
You can learn more about digital and sling psychrometers in this paper from MTestco. We offer the paint testing equipment needed to perform a safe and thorough inspection, as well as important guidance documents for out in the field. Contact us to learn more about our product lines.
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