Relative Mode on Protek 608 - Page 1
Forum section: electronics / testgear

author: rjk5378
author_rank: Contributor
timestamp: February 04, 2014, 08:06:51 pm
content: Hi. I seem to recall sometime back that there are some on here who have the Protek 608 multimeter. I have two of them and really like them, but I am having a problem with the relative mode. When I try to use the REL mode on the 608, no matter what value was in the LCD display when I first hit the REL button, all subsequent measurements read out -49.99 Megohms. The last two decimal places may vary a little, but the -49.9M is the same for several different test values I have tried.It could, I suppose, be operator error <g>, but I think I am doing this correctly. I take a measurement, e.g., shorting my leads together to get some very low result, e.g., 0.114 ohms, and while that value is still in the LCD display, I press the REL button. The REL indicator appears in the top row of the display, and the main display reading changes to 0.000. After that, if I take a measurement, the dispaly should show the value measured by the meter minus the 0.234 ohms. At least that's how I understand the 608 manual, and that is also how it works on other meters (e.g., the Extech EX430). But what I get is -49.99M, no matter what resistance I am measuring. I did this and then tried measuirng a 50 ohm resistor and a 2.975K resistor, but I still got -49.999M for the 50ohm and -49.997 for the bigger one. I got the same results when I tried these two resistors, rather than my shorted leads, as the relative values. It seems that no matter what resistance I set as the relative value, and no matter what resistance I then measure, the resulting readout in REL mode is always -49.99M.I tried this again, putting the Protek in low ohms mode first. Same results. Only difference is that in regular mode the display reads -49.000M, wheras in low ohms mode it only returns two decimal places, so I get - 49.99M.Curious about that minus sign, I tried reversing the probes--usually only worry about poarity on resistance measurments when using my Simpson 260 <g>, but either way the readout is *MINUS* 49.99M, whatever that means.At first I suspected my particular unit was faulty, but as mentioned, I have two different Protek 608 meters, and I get the same results with both units.Any insight into this would be much appreciated. Thanks.- Bob, KY3R

author: rjk5378
author_rank: Contributor
timestamp: February 04, 2014, 08:15:36 pm
content: CORRECTION:>>Only difference is that in regular mode the display reads -49.000M, wheras in low ohms mode it only returns two decimal places, so I get - 49.99M<<I meant to say in regular mode it reads -49.999M. Sorry. Fat fingers! <g>

author: thmjpr
author_rank: Regular Contributor
timestamp: February 08, 2014, 05:44:43 am
content: Same results. If you REL on 0V you also get incorrect readings (0V no matter what). But REL on say 20V works fine.I recall getting odd readings when the battery was low (before the low batt symbol was displayed). But I don't think that is the case here.

author: rjk5378
author_rank: Contributor
timestamp: February 08, 2014, 01:49:22 pm
content: Thanks. No, not battery. And since this is happening on both of my units (one of which is new) and your meter as well, seems to be a problem in the design itself. I can't get REL mode to work properly under any circumstances (resistance, voltage, small values, large ...). This must be a glitch in the actual logic circuitry used for this mode, which leads me to wonder if it also affects the "sorting" or "go/no-go" mode. I will check that later today.If this is a design flaw, it's amazing these units ever left the factory. This fault is obvious and easy to find. Unfortunately, Protek is no longer supporting these meters, so there's no one official to go to for help.Funny. I have a Fluke 27/FM. As old and beat up as it is, everything about it, including REL mode, still works exactly as it's supposed to. While I like the Protek and am impressed with its specs versus the price, this little discovery has convinced me to throw in the towel and get a Fluke 87. I mean, if you can't rely on your main test equipment with confidence, all bets are off! <g>-- Bob, KY3R

author: rjk5378
author_rank: Contributor
timestamp: February 19, 2014, 11:20:15 pm
content: Update. The retailer (Test Equipment Depot) confirmed that my newly purchased Portek unit was bad and offered to replace it. However, knowing that my used unit and a unit owned by another forum meber exhibit exactly the same behavior, I was soured on 608. So I instead had them give me a credit toward a Fluke 87-V which should be on its way to me now. I may or may not keep my used Protek--it seems to work properly except for the REL and GNG modes--but I'll probably end up selling it at a swap meet. I suppose you can never have too many multimeters, but I think I can live without Proteck and somehow make do with my remaining collection that now includes three Flukes! <g>I would, however, be curious to learn if this is a flaw in every unit of this model, or just a particular batch. The three units I have info on have this problem, but there may be a properly working unit out there somewhere.

author: rjk5378
author_rank: Contributor
timestamp: February 19, 2014, 11:27:13 pm
content: Quote from: thmjpr on February 08, 2014, 05:44:43 amYes. I did some more testing, and curiously found that values around 20 volts and also 5 volts volts worked fine, but not other voltages I tried, including low values near 0 volts. Oh well. I returned my newly purchased unit, and will have to decide whether to keep the used one I've had all along.