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Adjusting Level & Span Manually

Last week we discussed how to adjust level and span automatically and when that feature is best used. While using AUTO can be very convenient in many situations, you’ll quickly find times when MANUAL adjustment is essential, either to getting the best image or understanding what you are seeing.

Use AUTO adjust to get “in the ballpark. The problem is, when you have a large span of temperatures—cold to hot in the case—there is little detail in any single cup.

How does MANUAL work?

Although it takes a bit of button pushing to get there, using MANUAL adjustment is not difficult and you’ll quickly learn how to do it without thinking. The current mode you are using is displayed in the upper right corner.

Many models of Fluke imagers are have a great feature designating the F1 key, when held down for several seconds, to toggle between AUTO and MANUAL modes. You can also quickly get to MANUAL by pressing the F2 key until the menu choices show MANUAL or AUTO. Either way, just press the F2 key again or until you reach the options for LEVEL or SPAN and then INCREASE or DECREASE.

I find it easiest to adjust SPAN first to what I think will be most useful.

When does MANUAL work best?

• I use the MANUAL feature when I know I’ll need a very narrow span. For example, if I want to trace down the location of heating in an electrical component, I’ll set the SPAN at a minimum and then increase LEVEL until only a small visible area is left in the image.

• If I have a good idea of what the difference temperature should be, say between insulated and uninsulated areas, I can adjust the SPAN to that difference and adjust LEVEL to the temperature of the insulated wall; the uninsulated areas will then show as warmer or colder depending on the direction of heat transfer.

• Whenever I’m looking at a situation where temperatures are changing, such as a steam trap cycling, and I want to determine exactly when they reach a certain level, I can fix both SPAN and LEVEL manually and watch for the object or process to show up.

• If there are extraneous objects in the field of view that will cause the AUTO function to adjust poorly, I can adjust manually exactly as I’d like the image to be.

When I use MANUAL mode, I can adjust SPAN to be quite narrow and LEVEL appropriate to each cup individually. The result is amazing detail in each cup.

What are the limitations of using MANUAL?

Using the MANUAL adjustment mode is not as fast as AUTO. I guarantee you will get tired of pushing buttons on some jobs! There will also be times when you’ve adjusted the image so that you can understand what you are seeing but, overall, the image will not be very good looking or even understandable to a non-thermographer. In such cases two images may well be needed, one adjusted manually showing the exact problem and another adjusted more broadly, either manually or automatically, showing the problem in the overall context.

SPAN and LEVEL adjusted appropriately for this cup.

How can I use MANUAL successfully?

All thermographers must master using MANUAL adjustments or they end up missing a great deal. There is simply no way around it. Practice on the same three cups of water I talked about last week. Interestingly, you will find that the best MANUAL adjustments are often very similar to what you achieved with AUTO when you moved in close and excluded extraneous objects. Remember, if the MANUAL adjustments are not working for you, just switch briefly back to AUTO to see what is going on or drop the image into Smartview and optimize the settings there.

SPAN and LEVEL adjusted appropriately for this cup.

Next week we’ll talk about a really great feature available on many Fluke imagers, 1-time auto adjust.

Thinking Thermally,

John Snell—The Snell Group, a Fluke Thermal Imaging Blog content partner

1 comment to Adjusting Level & Span Manually

  • John Snell

    Please note in each of the 3 images of single cups, I could have narrowed the SPAN setting even more and let the table become saturated. This would have given even more thermal detail in the liquid and the cup itself.

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