IEEE Consultants' Network of Long Island

Dual-Resonance Coil Testing - John Dunn, Consultant, Ambertec, P.E., P.C.

If you need to measure a transformer winding inductance in situ, while the transformer is all hooked up to its operating circuitry, that surrounding circuitry may interfere with getting the measurement done if there is a large capacitance present across the winding in question. An LC meter I once tried to use in that way simply could not ascertain a transformer winding's inductance because there was a large capacitance being reflected into that winding from the transformer's other windings.

However, there is a way out of this problem using the test fixture as sketched below. 

Type-K Thermocouples - John Dunn, Consultant, Ambertec, P.E., P.C.

Thermocouple tables are published from which you find the relationship between millivolt (mV) measurements and thermocouple temperature, typically in degrees C. That relationship between temperature and mV, in the case of a type-K thermocouple, happens to be approximated as an 8th-order polynomial.

The GWBASIC program below uses that polynomial to find an approximation of thermocouple mV output given a specific temperature in degrees C. This can be useful in making simulations where you really don't want to have to deal with a real device sitting on your workbench at multi-hundreds of degrees.

Some tabulated results from this program are as follows:  

Diode Dynamic Impedance - John Dunn, Consultant, Ambertec, P.E., P.C.

A diode can be used as a variable attenuator element based on variability of the diode's dynamic impedance versus its bias. An estimate of that dynamic impedance can be found from the basic diode equation as follows: 

 
 

Padding Around with Attenuators - John Dunn, Consultant, Ambertec, P.E., P.C.

These two configurations of attenuator pad are undoubtedly familiar, but finding their resistance values for some particular dB of attenuation can be a little inconvenient. 

Using Recursive Differential Equations - John Dunn, Consultant, Ambertec, P.E., P.C.

This circuit is a simple RC network being charged from a DC source for which a descriptive, first order differential equation is written and is then put into a software loop to simulate the actual process under consideration:

 

Your clock battery still matters - by Dave Rost

PC Problem:

On Tuesday, I turned on my computer and was sent to CMOS with a note about the clock. I found the clock a few hours off and an incorrect date. I fixed this and continued on my way with no further problems. I got the same complaint on Wednesday, but after fixing it, I got a complaint about a bad system disk, which certainly gets one’s attention. I stuck in my Windows XP emergency floppy and got a DOS prompt. I have two hard drives; one (“C”) has Windows and several partitions, the other (“D”) has my data in two partitions. A little changing of directory and directory checking revealed that the “C” and “D” drives had become reversed.

I got out my Acronis emergency disk and attempted to change the drive letters. They seemed to change as requested, but when I left Acronis, they reversed again. After several repeats of this, I opened up the computer case. Reseating the cables on the hard drives had no effect. After I unplugged the data disk, Windows loaded normally, and I was able to use my file management program (Ztree). All logical drives on the system disk were present. The data disk was not shown (as would be expected); the interesting thing is that there was no “D” drive; higher lettered drives were not re-lettered; there was a gap between “C” and “E”.

Fitting Exponential Equations to Data - John Dunn, Consultant, Ambertec, P.E., P.C.

Most physical processes in nature have exponential properties. Radiation half-life is one example, thermal transitions from hot to cold or cold to hot are another example.

Often, a set of data from some process can be a little messy, a little noisy. However, if the data points look exponential, the underlying process is probably exponential and its fairly easy to find an equation for that exponential behavior:

We can go from this:  

to something that looks like this: