Member postings for Colin Whittaker

The oilfield has some amazing units ...

The volume of a reservoir uses acre feet.

Density comes in lbs per US gallon.

And gas rate is Mscf/d where the M stands for a thousand and the scf is a standard cubic foot.

The standard cubic foot of gas is measured at standard temperature and pressure. But which standard, there are more than half a dozen in use around the world.

API oil density is measured using an obscure inversion chosen to give a linear scale on a hydrometer.

(You'll never guess where I used to work.)

Anybody here encountered OD tape? Used to be quite common in the oilfield. Tape was marked in inches divided by Pi. Wrap the tape around a tubular and read off the OD directly.

Continuing on the dead weight tester pressure calibration story ...

Besides making a correction for latitude there is also a correction for altitude as the atmospheric pressure drops. For example, back in the early 1990s, 4,500 ft up in the Southern Highlands of Papua New Guinea, I found I'd spent 2 years calibrating my strain gauges 2 psi high (or was it low?).

Happy new year..

Murray,

I never thought to disavow DC electrolytic capacitors; it seemed too obvious. Just goes to show the danger of giving electrical advice on forums like this.

As you say, if the manufacture quotes an AC voltage rating then you don't need to do any further calculations. (My last high voltage exercise was connecting 230V phase to phase with a very high voltage capacitor to try and encourage my Powerline LAN plugs work throughout the house. Target voltage rating >230*root3*root2V.)

Cheers, Colin

230V is the RMS (root mean square) voltage. The peak voltage will be 230 * 1.4142 = 325V. The capacitor has to withstand the peak voltage with a safety factor. Anything greater than 400V rating should be OK.

Dave,

It was supposed to be a tongue in cheek comment but I guess I omitted the necessary smilicon.

But your friend's comment about Thai house electrics doesn't sound too wrong. I've given up trying to keep the house wiring correct and I'm concentrating on keeping it non-fatal.

The worst electrics I ever encountered was in Egypt. An electrician out there only needs one tool, square jaw pliers with plenty of scotch tape on the handles. Grub screws from switches and sockets are simply discarded and a bare wire inserted through the cable hole and back out of the grub screw hole and twisted back around itself. Earths? What's an earth? Fuses? No they keep on blowing? And don't get me started on the jointing of the paper insulated telephone trunk cables.

Edited By Colin Whittaker on 20/10/2016 12:42:41

Three meters for three phases!

Here in Thailand most big houses have a three phase power supply because of all the air conditioners. The three phase power is measured with a single three phase meter. I wonder why the UK is so backward?

Colin

Re the series connection of LEDs. I think you'll find that you can daisy chain LEDs of the same colour but the different colours will need different currents to deliver equivalent brightnesses, Hence a separate circuit for each colour of LED.

There was a comment about why would a single diode be used for half wave rectification.

The answer, I think, is that the particular generator used was voltage challenged and the 1.2V drop from a full bridge rectifier could not be tolerated while a 0.6V drop was just acceptable.

Managed to load it at last but it's very very slow. (While everything else on the internet downloads as fast as usual.)

Whoever is hosting your magazines must be having a bad network day.

Colin

Has the damp piece of string that connects ME and MEW to the internet broken again? Can see the forum posts OK but the magazines start to open and then just hang.

Problems I like; I trained as a problem solving engineer. One of the reasons for retiring was the replacement of problems with challenges.

And going off on a slight tangent, management, some 30 years ago, used to proceed along the lines of, "It's a challenge." "It's a chance to develop yourself." and in a very strong french accent, "You 'ave to do eet!" Can you guess who I was working for?

Colin

Here in Thailand if I want acid to reduce the swimming pool pH then I go to the local hardware store where they sell -1 pH hydrocholric acid. I'm amazed that I'm allowed to walk in and buy 4 gallon jerry cans of the stuff. The stuff gives me the heebie jeebies as I see it steaming from the open cap.

Tim, Slip of the finger. Precious metal, not rare earth. But the precious metal means a coating thickness measured in microns not thous. Any metal working abrasive will rip off that coating and fresh corrosion will shortly follow. If the repair is to be more than temporary then the contacts need cleaning.

The quick fix of the sandpaper (in the old days often the abrasive from a box of matches) was greatly deplored by the technical managers of the Strowger telephone exchange I worked in.

Colin

It is a very nice article in this month's MEW about fractional horse power induction motors. The only point that gave me a slight pause for a cringe was the idea of cleaning up the centrifugal switch contacts with sand paper. Almost all electrical switch/relay contacts have very fine coatings of rare earth metals to avoid corrosion and consequently high resistance. Sand paper will strip these coatings off and give a quick fix that rapidly deteriorates.

In the absence of a burnisher (I've only ever seen one once in my career, here's a link to what I mean, http://www.tecratools.com/product615.html) I'd suggest a toothbrush and contact cleaner. It's also useful to set up a slight wiping action on the contact.

There will be motors without special finishing on the contacts and these can be sandpapered but if you can't tell the difference between these contact types then err on the side of gentleness.

A very nice article Ted.

Colin

Being challenged for your age?

Recently a young lady offered me her seat on the train and my jaw dropped before I blurted out, "I'm not that old!" I mean I'm 59, I run, swim, cycle etc. so I guess she mistook the tweed jacket and flat hat for a sign of decrepitude.

Colin

Nitrile and Viton were the two commonest O'rings we used to handle downhole mud pressures of many thousands of psi in the oil business. Not sue that you'll get the slipperiness that you require though.

Colin

Guys,

A good earth keeps you safe. It doesn't prevent RCCB trips.

The RCCB (residual current circuit breaker) looks for an imbalance in the live and neutral line currents (due to a >30mA leak) and trips the breaker.

With the power off, wash, clean, dry and you should be good, as long as the cable isn't damaged elsewhere.

Colin

I agree with John, it smells like an intermittent commutator problem that may just need a bit of jiggling or spring retensioning to start working. It could also be a burnt out field or commutator winding, in which case a repair will normally be very problematic. If you are lucky then it may be the power switch.

Even with 40+ years of electrical experience I can still scare myself with live testing of appliances like this so I don't really want to suggest anything to someone with less electrical knowledge and quite possibly a weaker heart.

Cheers, Colin

Without a circuit diagram or any test equipment it is almost impossible to fault these kind of boards. What you can do is make a careful visual inspection for any discoloured components; resistors, transistors etc. and replace them. This may fix the problem but then again it probably won't.

Some of the soldered joints look a bit iffy (but that may just be the quality of the photo'. Retouching the joints with a soldering iron may cause normal operation to be resumed but then again it probably won't.

In my experience the best way of fixing a board like this is to first order the replacement. Then even the most trivial of home repair operations will see it working again.

Good luck, you'll need it, Colin