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Thursday, 13 November 2014

Do consumers really understand test instruments?

As an experiment, I recently posted a question on Amazon against a 'Microwave Leakage Detector' that sold for £10 compared to others that were selling for around £50. Not surprisingly the £10 seemed to be selling well and I was interested to see if customers were driven by price only. Below are the answers from customers and my views on this.
The question I posed was ' What is the fail threshold? Does this drift with time?'  The answers I got were as follows.

Answer #1
Cannot really answer the question.
I bought this item to test my daughters microwave after popcorn burnt in it.
The heat did not cause much visable damage but I was concerned about the door surrond distorting.
On using this tester, I found the seal was indeed leaking and so condemmed the microwave.
I have susequently tested other machines and they all 'passed.'
As for the technical details, I have no idea.
I was just happy to find the leaking microwaves and so avert possible damage to her health.
For the price it did the job. If you required a difinitive tester I would suspect the cost will be high.'
Answer #2 Perhaps it depends upon what you want the detector for. If you want professional quality then you need to spend quite a lot of money. If, however, you just want a gadget that will allow you to occasionally check a family microwave then I would say that this one is fine. I can't think of any way that the fail threshold could drift because the device is simply a coil in which stray microwaves generate a small electrical signal. However, all it will do is tell you whether there is any leakage and whether that exceeds safe limits. A professional model would yield much more information that the average layman wouldn't need or, possibly, even understand! Answer #3 You need the expertise of a specialist, Iam not one Answer #4 You would need a microwave expert to answer these two questions.   Answer #5Truthfullly, unless the door is damaged, there shouldn't be a problem. I don't think anyone can answer questions like this except the manufacturer. Under normal conditions, as long as you are a foot away from the microwave when it is on, there shouldn't be any issues. This item will only measure leakage when pressed up against the microwave.   Comments  Any test instrument that says PASS or FAIL must first of all make a measurement and then decide whether this was OK or NOT. In order to take this decision, it has to have an internal set threshold. If it measures signals above this then this is a FAIL and it measures signals below this it is a PASS.  Customers need to be suspicious of a tester that does not tell you what this threshold is. For example, if this threshold is set high, then it is going to PASS faulty appliances. If it is set too low then it is going to FAIL perfectly good appliances.   This has nothing to do with price - it's to do with whether it's fit for purpose or not. Anyone remember the 'Fake Bomb Detector' story? That shows that you can indeed fool a lot of people most of the time.  I also found the comment 'I can't think of any way that the fail threshold could drift because the device is simply a coil in which stray microwaves generate a small electrical signal ' quite worrying. All it would take is mechanical damage to the coil in which case it will end up PASSING all appliances, even faulty ones.  My earlier blog titled 'When is a PAT tester not a PAT tester' mentioned a tester that had a PASS limit 100 times (10 ohms instead of 0.1 ohms) the recommended one which would end up PASSING faulty appliances.   Summary    Most customers are trusting and will assume that testers offered for sale are fit for purpose. It is upto the professionals in the industry to make sure that we do not abuse this trust.     

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