Microamp readings with DMM...do you ever get steady reading?

JUGHNE

I have a HW R4795A on a "Adams Speedflame" NG power burner. It is on a small 1961 Kewanee23.6 HP hot water boiler.
There are about weekly lockouts on flame failure. This control will re-try once for restart.
The R4795 has a green flame amplifier R7289A card installed. It calls for 2 microamps minimum for a flame rod.
With pilot or main burner on the reading varies from less than 2 up to 4. As the DMM counts out numbers it goes from the range of low of 1.3 or so to 4. I have a good average around 2 but no steady reading.
I have tried 2 different DMM, the cheaper one gives the higher readings of 2 to 4, the more expensive DMM shows only about 1/4 or 1/3 the readings of the cheaper meter. Considering that it takes a minimum of 2 to hold the gas on I trust the cheap meter. Both meters bounce constantly.

HW lit calls for a steady current, "meter does not vary more than a needle width".....of all the meters I have with needles, the lowest range is 0-50 microamps. 2 is pretty hard to read on that scale. Of course HW makes a meter just for this, W136.
What do you people use for measuring 2 Microamps?

I just cleaned the flame rod this season.
The flame rod cable has good ends.
The flame rod & cable check out fine with a megometer.
The connections on the R4795 have all been checked and are tight.
The burner is grounded thru several points and are connected eventually to "G" of the control.
The pilot NG regulator has been changed.

Any ideas are appreciated, Thanks.

EBEBRATT-Ed

I use a fluke 902 to read microamps. Used to have a W136 but no more.

I have found that whatever the minimum signal the mfg. tells you(Both Honeywell & Fireye) is usually the bare minimum IMHO you need more.

I prefer reading the signal with an analog meter if I have one. It reacts better to the bouncing.

I have been told that a minimum low signal is preferable to a higher signal that is bouncing.

That being said the real problem is the flame rod. I don't know why but I have spent 43 years befuddled by them. I have cleaned, scraped, grounded, adjusted and run separate ground wires and replaced parts and always have difficulty with them and just like your job struggling with a low signal.

If I ever put a meter on a flame rod job and had a high signal I would probably drop on the spot.

Good luck with the flame rod!!!!! If you find the flame rod secret I would love to know

If I had my way I would check into the possibility of converting it to Ultraviolet if that's possible.

Sorry I am no help on this

ratio

I use an adapter to measure μA with my digital multimeter. If it's left on autorange it occasionally wants to range up & down, but ranging it manually fixes that.

Solid_Fuel_Man

Will moving the rod into the flame stabilize your reading? If it's not in a good ionized portion the reading can bounce. Look at your ground to the chassis and burner, microamps are very small and any poor/marginal connections will present a problem.

Taylor

JUGHNE

The design of the flame rod bracket and burner design pretty well dictates its position. I did find a little ragged connection where the lead connects to the flame rod. Cleaning that up did help a little. I did reseat all ground connections. With main flame on the entire rod would be in the flame. It is now 2 to 4 microamps. Has not locked out since then. This has been going on for years. Some seasons no problem and others now and then.
What is amazing is that my mod con Lochinvar shows a solid 15.2 microamps when running. I suppose the internal electronics clean up that reading to make it steady. But that little 80,000 Btuh boiler really produces 15.2 while 500,000 power burner does 2-4. ?

Does the Fluke 902 give you much bounce on microamps?

Thanks for replies.

bob_46

I'm guessing you have a Q179A pilot. There is usually a band around the pilot burner head with some little fingers on it. The area of those fingers compared to the area of the rod determine strength. Are all the fingers there? I had one that drove me nuts it would never lockout when I was there. I got pissed and decided to lay on the floor and watch the pilot and cycle the burner until it failed or I died from old age. After a couple hundred tries I noticed one time the pilot didn't go completely out, the 4795 checks for flame at the start of it's cycle if it detects flame it locks out. I replaced the pilot solenoid and never had another problem. That's all I got.

JUGHNE

Thanks Bob, that is a good point to consider.
Actually have to remember that these controls will not light a fire if you already have one going.
I have had this one flame out on main burner and recycle for its one attempt and actually relight and carry on (twice). Those are a rare observation for both of our situations.

I am sure customers wonder why we might sit on a bucket or lay on the floor and observe, just waiting for that magic moment.

BobC

I remember working on a machine that had been down for almost a week. Different people had been working on the problem but nobody was able to put their finger on it. It was an intermittent fault that was hard to localize.

It was a Sunday and the mail volume was lighter than usual so I decided to put some time in on it. I had an idea it was in a specific are of the machine (140ft long and 25ft wide). After about an hour I confirmed it was in that area so started to look closer.

I determined it was in a large bundle of cables and started moving things around, I finally got it down to a 6 ft area and started pulling things apart. In the end I found a shielded cable that was buried in this bundle of wires that had a ground wire soldered onto the wires shield. Whoever soldered that wire on 9at the factory) left a needle like point that was digging into one of the conductors in that cable. After redoing the shield connection and using some shrink tubing to protect the punctured wire the machine was up and running.

No matter what your working on troubleshooting is pretty much the same. You zero in on the problem by discounting other probable causes one by one. You start out with maybe 50 possibilities and discount them one by one until all that is left is the actual problem.

Sometimes it takes 15 minutes and sometimes it takes a week or more.

Bob

EBEBRATT-Ed

Sometimes I wished I worked in a factory where I could take as much time as I wanted to troubleshoot.

Unfortunately in the contractors world the clock is ticking when we are on the job and that costs $$$$$$

I think looking for a meter that doesn't bounce the signal is counterproductive. The trick is to steady out and maximize the signal.

Which as far as flame rods go isn't a possibility in my world.

I m waiting for a "flame rod god" to tell me what to do because I have never been successful in improving a FR signal and I haven't found anyone yet who has come up with a solution.

Flame rods are popular because it is the one and only flame detector that is 100% fail safe. It cannot prove a flame when one does not exist.

Unfortunately in my world they don't work reliably although there are millions in use.

Harvey Ramer

I have a question. Do different flames/fuel mixtures or propane versus natural gas, have any effect on a flames continuity?

@Tim McElwain

BobC

You need a meter that has a filter on it to average everything out or an analog meter.

Digital manonometers can bounce around like a yo-yo also.

Bob

JUGHNE

Too much information for the meter and then it gets into some averaging/sampling mode and cannot give you a solid reading.

I think the early DMM would do this with simple AC readings and drive you nuts. The beauty of an analog meter is that it is a little slower to respond having to incorporate a mechanical function in its workings.

BobC, I know you know what a Simpson 260 is, was state of the art some decades ago.....it only has a 0-50 microamps scale.

However, I would not trade my run of the mill UEI meter for much. Do you recall what it took to check a capacitor in 1965? We had one in trade school, bench work only, quite involved set up and then watch a very small crt do it's thing.
I remember that and use today's DMM and am still amazed each time as it makes me recall that 1965 instrument.

Then digital manometers, necessary with 2 stage equipment, but just touching a screwdriver to adjust gas pressure almost affects the meter reading....but needed for accuracy.

It is all good and great and also annoying at the same time.

BobC

@JUGHNE The old capacitor checkers had a magic eye tube in them, they were made by Sprague in Adams MA. Back in the day they were pretty much what most shops had. If you were in the research lab end of things you used a bridge that you had to zero out, like the Genrad 65o which evolved into the 1650.

You could just use an instrumentation op amp to give you a gain of 10 and that would give you a 0-5ua scale on the Simpson 260 (I own 2 of those - one -2 and the other a -6). You just need a nice low drift chip and your all set. I worked for analog devices back in the early 70's, they published a great handbook that was a cookbook for stuff like that

Bob

JUGHNE

Yes, Bob I knew you would know...."magic eye" was the term, thank you.
Now imagine today's HVAC person having to use one......you would just change the cap out. But old caps used to last for 20 years easy or just blow up and that was a easy decision. Maybe PCB's made them last longer. I have a 50 MFD 440 VAC from the 60's that I keep for a spare, it has helped some stuck compressors take off. It is the size of a motorcycle battery.

bob_46

To check caps I hook them to 110, measure the voltage and current draw. Amps times 2650 divided by volts = MFD.
I'd have to dig out my w136 to check but the range I used for flame rods is damped, it says so next to the selector switch.

BobC

Sounds like the guy who designed that meter listened to people who actually use it.

bob