"Shunt" Resistors

s. In the last thirty years my measurements are all done by measuring volt age across series resistor. Is this resistor still referred to as a "shunt "? Even though it is no longer shunting current around a current meter, ob solete terminology often remains. An example is calling the AC-DC power su pply in an LED replacement for a fluorescent lamp a "ballast".

Yes, it is still called a "shunt" resistor as the resistor is in parallel w ith the meter, not the load, although they also refer to it as a "current s ense" resistor.

In the solid-state physics world (back when I was doing that) we solved the problem by annealing in _forming gas_, which is 98% N2 and 2% H2.

It won't burn in any mixture with ambient air, and for many things it works just as well as H2. Of course it doesn't always suffice, because some substrates react with nitrogen.

Thirty years ago, my late (and very dear) friend Don DeCain and I built a gizmo for finding micron-sized particles floating around inside hydrogen-filled belt ovens used for sintering ceramic and glass-ceramic substrates for IBM mainframes.

The ovens were about 30 feet long and 5-6 feet in height and width, and contained a conveyor belt down which the substrates travelled. They were about 100 mm square, with well over 100 layers. The original ones were alumina ceramic with (iirc) tantalum metal paste, which AFAIK never had a single field failure. Alumina has an epsilon of about 10, though, which slowed them down. (Later ones were glass-ceramic with copper wiring, which is a whole saga in itself.)

This was in IBM's East Fishkill plant, building 322, and that whole end of the building was made of blast doors--both walls and roof. At the time (1990ish), IBM was the world's second largest industrial user of hydrogen, after NASA. Every time a substrate came out, a door opened and a spout of fire came out.

It really was a lot like the throne room of the Great Oz.

Forming gas works for a lot of applications--less dramatic but much safer.

Cheers

Phil Hobbs

ors. In the last thirty years my measurements are all done by measuring vo ltage across series resistor. Is this resistor still referred to as a "shu nt"? Even though it is no longer shunting current around a current meter, obsolete terminology often remains. An example is calling the AC-DC power supply in an LED replacement for a fluorescent lamp a "ballast".

with the meter, not the load, although they also refer to it as a "current sense" resistor.

Interesting, but your source seems to be inconsistent with their terminolog y.

Definition shunt resistor A shunt resistor is used to measure electric current, alternating or di rect. This is done by measuring the voltage drop across the resistor.

They go on at great length to talk about "shunting" current around a more s ensitive current meter to measure higher currents. They also talk about "s hunting" current around something for other purposes such as a crowbar circ uit. I don't see them discuss using a voltmeter to measure the voltage at all although they do mention that a shunt can be specified with a current a nd a corresponding voltage rather than simply the resistance.

No matter. It just struck me odd the term was used this way. I've never c alled it a shunt resistor unless it was shunting current around a current m eter. I actually have much bigger problems with the guy. I don't have a r ig to test so he has to take measurements and provide them to me. He is re ally, really poor at understanding what is going on electrically. He doesn 't understand that he should see the same voltage at both ends of a wire co nnection for example. It makes it hard to know what to ask him to do somet imes because I don't know if it will produce anything useful. I've been tr ying for over a month to get him to take the measurements to verify the bat tery charger is working. He took some measurements that left out the input voltage from the power brick which is needed to know the current across th e "shunt" resistor measuring the input current. He also doesn't understand that an open collector output that has no pullup has to be measured to gro und with an ohm meter even though I've told him this half a dozen times in messages and verbally.

I would go on and rant about how he won't spend any time writing requiremen ts and make major changes after work has been done, but time is short and I need to get back to what I was doing.

Thanks for the link.

Academics want a lot of provable math. A real engineer does whatever it takes to make a thing work.

Yeah, as long as it works many times and not just once on the bench. :(

The most useful ad-hoc math aid is Finagle's Constant, which when multiplied by the answer you got gives the answer you should have gotten. (I once applied that by name in an undergraduate physics problem set, and got full marks. Cheers for TAs with a sense of humour.)

Tally-ho

Phil Hobbs

True. Equations tend to be reliable.

Since using the wrong word usually means that you haven't thought hard enough about what you are doing, it's usually not the the choice of word that they are getting prissy about. Sloppy engineers do go in for that sort of evasion.

Real engineers can use math to get something that not only works, but works pretty much as well as it could.

"An engineer is someone who can do with one dollar what any damned fool could do with two".

I've cleaned up after enough "whatever it takes" engineers to get pretty prissy about their habits.

:) Especially softies :(