How to Effectively Choose and Use Test Instruments

HVAC School - For Techs, By Techs

Bill Spohn with TruTech Tools joins us to talk about why being “approximately correct” is better than being “exactly wrong” when it comes to test instruments.

When you see a number, that doesn't necessarily mean that you're dealing with a number you're supposed to see. For example, nitric oxide can present as "false CO" to a carbon monoxide sensor. Test instruments that mistake nitric oxide as carbon monoxide will give a different reading than ones that don't pick up nitric oxide as CO, but that doesn't necessarily make either of them wrong. So, some instruments can give you false positives based on exactly what they measure.

On the other hand, false negatives may have to do with poor sensitivity. A common case happens with leak detectors; on occasion, a leak detector won't be sensitive enough to pick up a leak.

You can't just say that a set of numbers on an instrument absolves you of responsibility for errors; you must understand the instrument, what it measures, and its sensitivity to use it appropriately. Being rigid in terms of specifications is also a mistake when communicating with customers; customer satisfaction is the goal, and it's okay if their comfort needs deviate from the specifications a bit. Overall, accommodation and mental/financial investment in your tools are the keys; for the sake of the customer, we need to make acceptable compromises, and that's something you must factor into your measurements.

Bill and Bryan also discuss:

• NOx filtration
• Bacharach PGM-IR
• Personal protective CO detectors and overloading
• Laboratory-grade instruments vs. normal test instruments
• Getting valid wet-bulb readings and using sling psychrometers
• Analog gauge variables and inaccuracy
• Lab testing and controlled conditions
• Ductwork in conditioned spaces
• Flow hoods
• Using our senses
• Olfactory fatigue

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