Testing box

[cdynasty001]

Say you have a box with test points on it. A, B, C, D, E, F, G. It's plugged into an outlet with a power switch in the back turned on. You have a multimeter and an oscilloscope. You're asked to determine what is between A and B, then C and D. What do you do to determine it? You're not allowed to open up the box to see what's inside.

 

[fmtjfw]

Step 1:
Voltages between all pairs of Terminals:
A-B, A-C, A-D, A-E, A-F, A-G
B-C, B-D, ...
F-G
with the multimeter Note AC and DC readings. Use HIGH-Z and LOW-Z settings
With O-Scope same set of readings. (O-Scope can be used for High-Z readings) and measure frequency
Dual trace feature, if available, can look for lead/lag

Step 2: try to draw vector diagrams to look for 3-phase and / or lead lag from capacitors and coils. Look for different voltages between HIGH and LOW-Z for impedance components.

 

[GoldDigger]

The best you could do in any case is determine what the Thevinin equivalent of the circuit inside the box is.

I expect that the intent of the problem is that there is no externally applied power, so that there is only a battery inside the box, along with some network or R, C and L value components.

You would first measure all voltages statically, then using the scope and opening, closing and shorting various pairs of leads under test you could figure out whether you had parallel or series reactances between the battery and those output terminals.

The OP can answer his homework question by figuring out the exact procedures to use.

If this were an employment test, I would say it is in the same category as the four question set that starts by asking how you would put an giraffe into a refrigerator.

 

[JFletcher]

The best you could do in any case is determine what the Thevinin equivalent of the circuit inside the box is.

I expect that the intent of the problem is that there is no externally applied power, so that there is only a battery inside the box, along with some network or R, C and L value components.

You would first measure all voltages statically, then using the scope and opening, closing and shorting various pairs of leads under test you could figure out whether you had parallel or series reactances between the battery and those output terminals.

The OP can answer his homework question by figuring out the exact procedures to use.

If this were an employment test, I would say it is in the same category as the four question set that starts by asking how you would put an giraffe into a refrigerator.

You've piqued my interest; please elaborate. I'm sure my answer that involves a high powered rifle, a chainsaw, and a large walk-in isnt what they are looking for.

 

[GoldDigger]

You've piqued my interest; please elaborate. I'm sure my answer that involves a high powered rifle, a chainsaw, and a large walk-in isnt what they are looking for.

Your answer is not outrageous, but not the one wanted either.

Here is the series of four questions, with the answers invisible until highlighted.

Supposedly they were part of the job interview test that Arthur Anderson consulting used for many years. Four year olds got more correct answers than the candidates.
It is important to know that candidates were told the correct answer to each question before the next one was asked.
So be sure to only look at one answer at a time.

Q1: How do you put a giraffe in the refrigerator?

A1: You open the door, put the giraffe in, and close the door.

Q2: How do you put an elephant in the refrigerator.

A2: You open the door, take out the giraffe, put in the elephant and close the door.

Q3: Simba, the lion king, held a conference for all of the animals in the jungle. Only one did not attend. Which one?

A3: The elephant. He was in the refrigerator.

Q4: You come to a wide river in the jungle, which you must cross. But the river is the home of deadly, ravenously hungry crocodiles. How do you get across safely?

A4: You jump in and swim across. (!!???!!) Sure, all of the crocodiles are at Simba's conference.

 

[Strathead]

Say you have a box with test points on it. A, B, C, D, E, F, G. It's plugged into an outlet with a power switch in the back turned on. You have a multimeter and an oscilloscope. You're asked to determine what is between A and B, then C and D. What do you do to determine it? You're not allowed to open up the box to see what's inside.

Come on, this is the age of miniature electronics. Strap a small camera on a cockroach's back. They can get in anywhere. :lol:

 

[steve66]

We don't get a solution to your first puzzle before you post another one?

I was tempted to say the first puzzle was absolute nonsense, but I noticed it was similar to a black box problem.

And the second puzzle is even more like a black box problem.

We did these in college, however, I believe we only did problems with 2 port, 4 terminal networks. It's called "port theory", and the solution to a 2 port network is:

It is simple to expand the equations to the 4 port, 8 terminal box shown. So to solve for what's in the box, all you have to do is measure all the impedances between all the terminals. Put them in the matrix, and the equation will tell you the resulting currents for any applied voltages. (This assumes the box has no active components, and only passive components.)

Conversely, we can also apply a known voltage, measure the resulting currents, and determine the impedances Z. In practice, if I remember right, we normally short one set of terminals, and apply a voltage to a second set of terminals. Then most of the numbers in the equation reduce to zero, and it gives us one of the Z's. Short another set of terminals, and apply another voltage, and you get another Z. We just do that until we have all the Z's solved for.

Edit: Actually, if we don't care about terminals E, F, G , or H, it is a two port problem, and we just ignore those 4 terminals.

 

[rambojoe]

Your answer is not outrageous, but not the one wanted either.

Here is the series of four questions, with the answers invisible until highlighted.

Supposedly they were part of the job interview test that Arthur Anderson consulting used for many years. Four year olds got more correct answers than the candidates.
It is important to know that candidates were told the correct answer to each question before the next one was asked.
So be sure to only look at one answer at a time.

Q1: How do you put a giraffe in the refrigerator?

A1: You open the door, put the giraffe in, and close the door.

Q2: How do you put an elephant in the refrigerator.

A2: You open the door, take out the giraffe, put in the elephant and close the door.

Q3: Simba, the lion king, held a conference for all of the animals in the jungle. Only one did not attend. Which one?

A3: The elephant. He was in the refrigerator.

Q4: You come to a wide river in the jungle, which you must cross. But the river is the home of deadly, ravenously hungry crocodiles. How do you get across safely?

A4: You jump in and swim across. (!!???!!) Sure, all of the crocodiles are at Simba's conference.

I can answer all but #3 with one answer. with a rock as a weapon and a can do attitude!
a teen that was on my maintenance crew always used this answer for everything. after id give him the ol "I'm not amused" look it would always make me smile...
there. now this one is off topic! (I don't quite understand the OP's riddle...)