I've been meaning to ask you - what is the point in the initial IR test you are telling people is required? All one is wanting to ascertain is whether or not the resistance between the part and MET is greater than 23 kΩ, and one can get that answer by going straight to the standard resistance (what you call 'continuity') test.
This has come a lot later than I expected.
... and I lot later than I intended, but I kept forgetting to ask!
What you say makes sense but that is the best way to test. It's good to know that it is >1000MΩ. As I keep saying 23kΩ is just the figure derived from 10mA and, in a way, irrelevant as readings will usually be a few ohms or many megaohms. However, should the measurement be 0.00MΩ a check is obviously required.
I'm thinking aloud (and perhaps turning my question/comment on its head!), so please bear with me ....
Firstly, what I wrote is wrong if one is using an MFT like yours and mine (and probably many/most others). Its 'continuity' range cannot indicate whether resistance is above or below 23k, since the highest result it can give is ">2000Ω".
If one's only interest is in whether or not the resistance is, or is not, above 23k (we agree it's essentially arbitrary, but there has to be some specific threshold if one is to get a yes/no answer about bonding), then I could turn my question/comment on its head, since one could almost always achieve an answer to that question with the
IR range of an MFT such as yours and mine. Any answer of 0.03MΩ or above indicates that the resistance is at least 25kΩ (hence >23kΩ
. If the result is 0.01Ω or 0.00Ω, then one can be sure that the resistance is <23kΩ. Only if it gives a result of 0.02Ω is there uncertainty as to whether the resistance is above or below 23kΩ - and you/I would then have a bit of a problem with our 1652's (and probably many other MFTs), since all the 'continuity' range could tell us would be whether the resistance was above or below 2kΩ - so not a complete answer. If, as a separate question, one wants to know exactly how low a "<23kΩ" resistance is, one would obvioulsy undertake a 'continuity' measurement (and will get an answer, provided it is less than 2kΩ
.
If one were using a multimeter, even the cheapest and nastiest will give answers up to about 2 MΩ, and most that cost any significant amount of money will measure up to at least 20MΩ, maybe higher, and all will measure down to 1Ω, more often 0.1Ω. I would suggest that such a meter would really give us all the information one wants. If the resistence were 'low', it would certainly indicate whether it were above or below 23kΩ, and if it were high, I personally would think that knowing it was, say, >20MΩ was more than enough. You say that it would be 'good to know' that it was above 1000MΩ, but would that really mean anything more to you than >20MΩ??
As you say, in practice one is probably very unlikely to get answers between, say 5Ω and a good few MΩ - so it's almost a dichotomous answer one is looking for.
You may think telling people who don't know to do it may be a bit pointless but it's not really.
As above, I guess it depends upon what sort of meter they are going to be using. If a multimeter, then (IMO) they simply have to make a single measurement (using whatever range proves necessary). If they're using an MFT, then an IR measurement alone will usually suffice. In the one (extremely unlikley) inconclusive case (IR result = 0.02MΩ
, and/or if one wants to know exactly how low a "<23kΩ" resistance is [e.g. to ascertain whether it is below 50/(Ia*5)], then one undertakes a 'continuity' measurement - but that's a separate issue, and 'our' MFTs would only give an actual answer if it were <2kΩ (which it virtually always would be).
Does any of this make sense?
Kind Regards, John