(Off Topic) paging Brett...

[Sean McEntee]

     ...and anyone else that can answer this question, of course

     I'm currently taking an Introduction to Solar Energy course, as it is a course requirement for my Social Work degree.

     We conducted a lab a few weeks ago on the greenhouse effect on thermal solar energy units by measuring the absorption of solar energy by both bare aluminum plates and plates with a black finish, both covered and uncovered.  An interesting note in the experiment was that the temperature was measured by electrical resistance as opposed to any kind of temperature sensor.  This really piqued dad's curiosity, and subsequently mine as well, as to how that worked.  I asked Dr. Baques about it on Monday after class, and he explained that the resistance was measured through a resistor, which is affected by temperature at a constant rate, as opposed to exponential rates when electrical resistance is measured through most conductive and semi-conductive materials.   

     So now we have the question of "why".  Under what condition would electrical resistance be the preferred method of reading temperature as opposed to a temp sensor or some other means?  Brett, we figured that you, if anyone here, would have some insight, while we wait for Wednesday's class to roll around so I can pose the same question to my professor.  Any ideas?

Thanks,
Sean

[Brett Buck]

     ...and anyone else that can answer this question, of course

     I'm currently taking an Introduction to Solar Energy course, as it is a course requirement for my Social Work degree.

     We conducted a lab a few weeks ago on the greenhouse effect on thermal solar energy units by measuring the absorption of solar energy by both bare aluminum plates and plates with a black finish, both covered and uncovered.  An interesting note in the experiment was that the temperature was measured by electrical resistance as opposed to any kind of temperature sensor.  This really piqued dad's curiosity, and subsequently mine as well, as to how that worked.  I asked Dr. Baques about it on Monday after class, and he explained that the resistance was measured through a resistor, which is affected by temperature at a constant rate, as opposed to exponential rates when electrical resistance is measured through most conductive and semi-conductive materials.   

     So now we have the question of "why".  Under what condition would electrical resistance be the preferred method of reading temperature as opposed to a temp sensor or some other means?  Brett, we figured that you, if anyone here, would have some insight, while we wait for Wednesday's class to roll around so I can pose the same question to my professor.  Any ideas?

   What other temperature sensor would you propose? The professor gave the right answer - the materials used in thermistors is particularly strong and repeatable (from unit-to-unit) temperature coefficient compared to, say, semiconductor junctions. Note that you can get them either way, either where the resistance down with temperature, or up with temperature. Typically, for temperature sensing, you use a one with a negative temperature constant (a thermistor). You either put a voltage across it, then measure the current, or put a constant-current source across it and measure the voltage. The latter is generally easier to deal with because all you have to do is measure the voltage (using an A/D convertor).

  Almost every electronic temperature sensor you run across is a thermistor at the root of it, they are cheap, reliable, easy to condition (set up a circuit to measure the voltage or current). No two semiconductor junctions work the same way or response the same way to temperature, you can envision other systems like a bimetallic strip that rotates a potentiometer - which has all the same electronic parts, but also a fragile and wear-prone mechanical system. Perfectly adequate solid-state thermistors can be produced and sold for 1/4 cent a piece in bulk.

    Brett

   

[Sean McEntee]

     Boom, there it is.  Thanks for the explanation. Won't have to hold Dr. Baques back from his lunchbreak tomorrow.

[Brett Buck]

     Boom, there it is.  Thanks for the explanation. Won't have to hold Dr. Baques back from his lunchbreak tomorrow.

  BTW, thermistors are used for other purposes, too. The most common other use is as a inrush current limiter on electronic devices. When you first turn something on, there are components that require a one-time "charge" (capacitors), and when the device has been off for a while, they are completely discharged, and when power is applied, they look like a nearly dead short briefly as they charge up. the dead short generates a temporary spike of current called the inrush current. On some things (old tube TVs, for instance), all this current flying in there caused an audible sound, a temporary "buzz" or other tone, and sometimes, the high magnetic field pulled the metal case of the cabinet in and cause it to thump like a drum head.

     Putting a thermistor in series, the thermistor starts off at room temperature and high resistance, limiting the current going in. Then, as the current goes through it, it heats up, and the resistance drops as a result, and then subsequently has little effect on the operation. Since they are taking the load, and run hot by design, they also tend to be the least reliable part (along with the electrolytic capacitors that cause the effect in the first place),

     Brett

[Tim Wescott]

Brett's leaving out thermocouples.

For industrial usage, the standard for room-ish temperature measurement is a platinum resistor (that's probably "the" resistor used in your experiment).  Good ones are a -- uh -- bit more expensive than a plain old resistor.  For high temperatures it's a thermocouple, which actually generates a voltage when there's a temperature differential across it.

[Dave Harmon]

  BTW, thermistors are used for other purposes, too. The most common other use is as a inrush current limiter on electronic devices. When you first turn something on, there are components that require a one-time "charge" (capacitors), and when the device has been off for a while, they are completely discharged, and when power is applied, they look like a nearly dead short briefly as they charge up. the dead short generates a temporary spike of current called the inrush current. On some things (old tube TVs, for instance), all this current flying in there caused an audible sound, a temporary "buzz" or other tone, and sometimes, the high magnetic field pulled the metal case of the cabinet in and cause it to thump like a drum head.

     Putting a thermistor in series, the thermistor starts off at room temperature and high resistance, limiting the current going in. Then, as the current goes through it, it heats up, and the resistance drops as a result, and then subsequently has little effect on the operation. Since they are taking the load, and run hot by design, they also tend to be the least reliable part (along with the electrolytic capacitors that cause the effect in the first place),

     Brett

Yep.....I got a pile of them in my Ham transmitters....in each primary leg of each transformer.
Occasionally the cabinet bangs so I probably need a higher cold resistance thermistor.....and....I'm probably not waiting until they cool off....too quick on the switch.

[Brett Buck]

Yep.....I got a pile of them in my Ham transmitters....in each primary leg of each transformer.
Occasionally the cabinet bangs so I probably need a higher cold resistance thermistor.....and....I'm probably not waiting until they cool off....too quick on the switch.

     Maybe, one of the most risky things you can do with some of these electronics is turn them off, then immediately back on again. It's really bad in tube audio amps. And yes, unless you allow the thermistor to cool off again, it just doesn't do much useful.

    Still, all you are trying to do is knock the edge off the current, not stop it, and reduce the stress on turn-on. Depends on what vulnerable parts you are trying to protect -  diodes rated for the "run" current or rectifier tubes that tend to flash over. Most of the other stuff will handle tremendous overcurrent for brief periods. A transformer, for example, even one with pretty fine wire, has to be heated above the melting point, which doesn't take long, but will handle a few milliseconds, and the back EMF is a limiter.

   These limiters work to first approximation, but when people working on electronics learn about them, they tend to go overboard. A case where it is important is when a tube rectifier is replaced with a semiconductor diode. A tube rectifier works much like a thermistor, it is a near open circuit/infinite resistance when cold, and as it heats up, very gently charges up the capacitors. Replace that with a silicon diode, you get instant voltage across the capacitor and whatever current the net resistance allows, and, slamming high voltage to/across all the other cold tubes. That's why guitar amps have soft-start switches, and why plug-in replacements for various tube rectifiers usually contain a CL-90 or other similar thermistor. A better solution is to leave the tube rectifier and put silicon diodes in series with the plates - the diodes do the rectifying and the tube  is a soft-start device. If a diode fails short, you are left with the tube for a rectifier. Rectifier tubes are a real weak point, do this, they last indefinitely.

    Brett

[Fredvon4]

I am quite surprised that Bret and others in this crowd did not question why a student of social work or psychiatry would have mandatory classes in this field .... at university level.....My merger knowledge in Science, chemistry, and physics leads me to believe too many entities are playing games in the wind, solar, and most other renewable energy endeavors.

Not questioning this class or the science being explored, and perhaps Sean just had to take it for matriculation reasons....but still smacks of "social engineering" to me

The skeptical Fred

[Brett Buck]

I am quite surprised that Bret and others in this crowd did not question why a student of social work or psychiatry would have mandatory classes in this field .... at university level.....My merger knowledge in Science, chemistry, and physics leads me to believe too many entities are playing games in the wind, solar, and most other renewable energy endeavors.

Not questioning this class or the science being explored, and perhaps Sean just had to take it for matriculation reasons....but still smacks of "social engineering" to me

The skeptical Fred

  I did wonder about that, but, Sean asked a specific question.

      Brett

[Sean McEntee]

I am quite surprised that Bret and others in this crowd did not question why a student of social work or psychiatry would have mandatory classes in this field .... at university level.....My merger knowledge in Science, chemistry, and physics leads me to believe too many entities are playing games in the wind, solar, and most other renewable energy endeavors.

Not questioning this class or the science being explored, and perhaps Sean just had to take it for matriculation reasons....but still smacks of "social engineering" to me

The skeptical Fred

A valid question that even my academic advisor asked when I registered for my fall classes.  Matriculation is pretty much it.  Between my JST and all of the smatterings of college that I took through the years, I only have a few "general education" courses that I need to take before I start in on major courses.  Among those is a physical and natural science class and a natural science class with a lab component. 

The solar energy class fills the science with lab requirement.  No politics or social engineering involved, just how the stuff works, and Dr Baques doesn't beat around the bush about the (many) limitations and shortcomings of both solar thermal energy and photovoltaics.  There's a big push here in CO on gov't-installed solar panels.  He pointed out the fact that 3/4 of the houses in Colorado Springs alone aren't oriented in such a way that they would be effective anyway. 

Physics in Everyday Life satisfies my natural science requirement.  No heavy math involved; just theoretics mostly.  Funny story: an end-of-course project is required in the form of either journal entries, a thematic essay, or "physics for Grandma" in which one has to explain the course material in terms that their grandma can understand, with weekly contributions due based on the week's lessons.  Needless to say, my thematic essay is on aviation: full scale, unmanned and models.  About a month ago, we studied the principles and laws of angular and circular motion, and my professor messaged me that he was very eager to see how I could apply that to aviation.  Let's just say I had an ace up my sleeve.

Again, everyone including my academic advisor asked why I was taking these courses in particular, and it's simply because they're more interesting to me than biology or geology or any of the "do it to graduate" courses.  With those are out of the way, however, next semester will be full up with sociology, psychology and social work classes, so it'll be time to really get to it on my major.  One of those classes is Social Work with Military Families.  That one shouldn't be hard...

Cheers,
Sean

[Tim Wescott]

...  With those are out of the way, however, next semester will be full up with sociology, psychology and social work classes  ...

Wait, are you going into social work, or training to be a truly effective Evil Overlord?

[Dan McEntee]

Wait, are you going into social work, or training to be a truly effective Evil Overlord?

     He already had that gig as a SFC in the Army!!

     Type at you later,
     Sean's Dad

[Brent Williams]

   These limiters work to first approximation, but when people working on electronics learn about them, they tend to go overboard. A case where it is important is when a tube rectifier is replaced with a semiconductor diode. A tube rectifier works much like a thermistor, it is a near open circuit/infinite resistance when cold, and as it heats up, very gently charges up the capacitors. Replace that with a silicon diode, you get instant voltage across the capacitor and whatever current the net resistance allows, and, slamming high voltage to/across all the other cold tubes. That's why guitar amps have soft-start switches, and why plug-in replacements for various tube rectifiers usually contain a CL-90 or other similar thermistor. A better solution is to leave the tube rectifier and put silicon diodes in series with the plates - the diodes do the rectifying and the tube  is a soft-start device. If a diode fails short, you are left with the tube for a rectifier. Rectifier tubes are a real weak point, do this, they last indefinitely.

    Brett

When using this series tube/silicon diode method on the rectifier, is there still a upper limit on the amount of filtering capacitance that can used?  I know in old Fender amps that had a 5Y3 rectifier tube, the first filter caps are like 8 or 16uf effectively.  Amps with a GZ34 rectifier had around 25uf effective.  Higher wattage amps that came with solid state rectifier diodes had around 40or50uf effective and big powerful 100w Marshall amps had around 100uf or more.  I was always told that the tube rectifiers in general have troubles with high capacitance filter caps, hence the lower values, but I can't remember the reasoning.

Also, does the silicon diode in series affect the total rectification factor?  5y3 can do 1.1 times incoming voltage, 1.2 for 5u4g, 1.3 for GZ34 and a silicon diode will do 1.4 times the incoming voltage on its own.

[Brett Buck]

When using this series tube/silicon diode method on the rectifier, is there still a upper limit on the amount of filtering capacitance that can used?  I know in old Fender amps that had a 5Y3 rectifier tube, the first filter caps are like 8 or 16uf effectively.  Amps with a GZ34 rectifier had around 25uf effective.  Higher wattage amps that came with solid state rectifier diodes had around 40or50uf effective and big powerful 100w Marshall amps had around 100uf or more.  I was always told that the tube rectifiers in general have troubles with high capacitance filter caps, hence the lower values, but I can't remember the reasoning.

 
    The reason is that the larger the filter capacitors, the more current they sink on startup, and as the voltage goes up and down after rectification. Your values sound pretty small. When I can find it, I will look in an RCA Receiving Tube Manual and see what they recomment. I *think* for a 5Y3 and a resistor-only pi network, I want to say it recommends no more than 40 Mfd. 8 or 16 seems more appropriate for a pi network using a choke.  More doesn't necessarily help, if the hum is acceptable, adding more doesn't accomplish anything. If it needs to be better, add a regulator.

   Having said all that, a lot of tube audio amps with 5U4, 6X4, and 5AR4 rectifiers use *much* more than the recommended maximum with reasonable reliability, like 220 Mfd for a 5AR4 with a big choke, as long as you avoid the rapid off-on sequence. Same issue - at some point, more is not better, and all of my tube amps use regulated B+.

Also, does the silicon diode in series affect the total rectification factor?  5y3 can do 1.1 times incoming voltage, 1.2 for 5u4g, 1.3 for GZ34 and a silicon diode will do 1.4 times the incoming voltage on its own.

    It knocks .7 volts off of B+, or, far far less than the variation from typical line voltage variation. But again, use a regulator. 

        Brett

[Carl Cisneros]

Sean:

Your subject of PHYSICS FOR GRANDMAS sparked a memory cell in my head this morning.

Back  in about 1972, one of the NCO's as well as myself (SSGT at that time) were given the task of writing a short brief
on how Inertial Navigation System works (for the new student) when I was stationed at Keesler AFB instructing Doppler, Inertial Nav and OTHER types of systems at one of the tech schools there.

I actually still have it here and can scan it and put it here if you would like. Our NCOIC's were not that impressed with it, but when we sent the
brief to Litton Industries (the manufacturer of the F-4's INS system), they loved it.

Carl

[Ken Culbertson]

Our NCOIC's were not that impressed with it, but when we sent the
brief to Litton Industries (the manufacturer of the F-4's INS system), they loved it.

It was a question on the xxx70 exam if I remember.  "One of your subordinates does an excellent job.  You are (A) Impressed and Commend him, (B) Not impressed and do nothing, (c) Tell him it is inadequate and then pass the work on claiming credit for yourself.  Answer of course was "C".   Different AFS, same rank.  I have been there and done that and I think it was in '72.  Operating manuals for the three-barrel version of the M-61 (M197) for the AU-24 Helio Stallions at Eglin. 

Ken

[Carl Cisneros]

Here it is Ken and Sean===============

We actually did this originally in 1971.

Think Brett might really like this.

The aircraft knows where it is at all times.  It knows this because it knows
where it isn't.  By subtracting where it is from where it isn't, or where it
isn't from where it is (whichever is the greater), it obtains a difference, or deviation.

The Inertial Guidance System uses deviations to generate error signal commands
which instruct the aircraft to move from a position where it is to a position
where it isn't, arriving at a position where it wasn't, or now is. 
Consequently, the position where it is, is now the position where it wasn't;
thus, it follows logically that the position where it was is the position where it isn't.

In the event that the position where the aircraft now is, is not the position
where it wasn't, the Inertial Guidance System has acquired a variation.
Variations are caused by external factors, the discussions of which are beyond
the scope of this report.

A variation is the difference between where the aircraft is and where the
aircraft wasn't.  If the variation is considered to be a factor of significant
magnitude, a correction may be applied by the use of the autopilot system.
However, use of this correction requires that the aircraft now knows where it
was because the variation has modified some of the information which the
aircraft has, so it is sure where it isn't.

Nevertheless, the aircraft is sure where it isn't (within reason) and it knows
where it was.  It now subtracts where it should be from where it isn't, where
it ought to be from where it wasn't (or vice versa) and intergrates the
difference with the product of where it shouldn't be and where it was; thus
obtaining the difference between its deviation and its variation, which is
variable constant called "error".

[Ken Culbertson]

Here it is Ken and Sean===============

And now you understand why they put curtains on the F-111 windshield.

Ken

[Sean McEntee]

Wait, are you going into social work, or training to be a truly effective Evil Overlord?

**maniacal laughter**

   I loved flying, but a close second was helping and taking care of people.  "Taking care of Soldiers" was the buzz phrase but I didn't like that because Soldiers are people and it's very easy, in navigating the pratfalls of leadership, for leaders to lose touch with their own humanity, let alone overlook the humanity of others.  As empathetic as I was, compared to my peers, my outlook changed greatly after my own behavioral health issues and treatment.  Behaviors that we typically brushed off as lack of discipline or some such thing were really signs of anxiety and/or depression.  When I was relieved as platoon sergeant (which parallels social worker in many respects) while I was undergoing my MEB, I more or less became the company counselor; taking on Soldier issues as I happened onto them and, with my fresh perspective, was fairly successful.  All of this got me interested in psychology, but in talking to all of my therapists and behavioral health providers, they encouraged me to pursue a career in clinical social work, an ever-growing field these days that would still put me where I wanted to be.  My last therapist that I saw while in the Army really sealed the deal for me.  He came from an Army background, and having a PCM that understood the in's and out's of the Army was incredibly helpful.  So that's my goal: a BSW in Social Work with a minor in psychology, an MSW in Social Work with a minor in psychology and sub-focus in trauma, and a GS11 slot as a Social Worker, for which there is a great need.  I can go on usajobs.com on any given day and there are at least a half-dozen DoD openings for Social Workers on Ft Carson alone.   One that is always open is a SW position with 10th Special Forces Group.  That position requires a TS-SCI clearance and a "willingness to travel to austere environments".  After 62 months in faraway lands, I can think of much better ways to make $140k/year.  Anyway, that's my post-Army plan.

     He already had that gig as a SFC in the Army!!

     Type at you later,
     Sean's Dad

I could tell you how right you are, but then I'd have to kill you

Here it is Ken and Sean===============

We actually did this originally in 1971.

     That's a pretty neat explanation.  I don't care what your NCOs say, it gets this NCO's stamp of approval!  There were some kids that I had under my charge that needed things dumbed down to that level.  Both the RQ-7B and MQ-1C had a pseudo-INS system that supplemented GPS navigation.  Since the GPS refresh was pretty long--about 7 seconds if I remember right--INS maintained precise location reporting in between GPS position updates.  However, in the instances that GPS was lost (and I had a few due to hardware failures), INS position became less accurate.  Over time, I learned that I had about 2 or 3 minutes before the INS fix became nothing more than a guess.  I had that time to find a road and use map-to-video to get home...it was like road-tripping 30 years ago with a road atlas.

[dale gleason]

That INS document was very important to thoroughly understand in a previous job I held. I kept a copy close by whenever making ocean crossings via INS- just in case. Then I lost it in the excitement, never to be seen again.

Thanks for bringing it back... I printed a copy and placed it in my brain bag, which hasn't been used in twenty+years.

I feel better now.

dg

[Brett Buck]

Here it is Ken and Sean===============

We actually did this originally in 1971.

Think Brett might really like this.

The aircraft knows where it is at all times.  It knows this because it knows
where it isn't.  By subtracting where it is from where it isn't, or where it
isn't from where it is (whichever is the greater), it obtains a difference, or deviation.

The Inertial Guidance System uses deviations to generate error signal commands
which instruct the aircraft to move from a position where it is to a position
where it isn't, arriving at a position where it wasn't, or now is. 
Consequently, the position where it is, is now the position where it wasn't;
thus, it follows logically that the position where it was is the position where it isn't.

In the event that the position where the aircraft now is, is not the position
where it wasn't, the Inertial Guidance System has acquired a variation.
Variations are caused by external factors, the discussions of which are beyond
the scope of this report.

A variation is the difference between where the aircraft is and where the
aircraft wasn't.  If the variation is considered to be a factor of significant
magnitude, a correction may be applied by the use of the autopilot system.
However, use of this correction requires that the aircraft now knows where it
was because the variation has modified some of the information which the
aircraft has, so it is sure where it isn't.

Nevertheless, the aircraft is sure where it isn't (within reason) and it knows
where it was.  It now subtracts where it should be from where it isn't, where
it ought to be from where it wasn't (or vice versa) and intergrates the
difference with the product of where it shouldn't be and where it was; thus
obtaining the difference between its deviation and its variation, which is
variable constant called "error".

    I particularly enjoy the frequent use of triple and quadruple negatives!   I *hope* my explanations of similar systems to our newbies doesn't sound like that, but based on the glazed looks, it probably does.

     Brett

[Dave Harmon]

    I particularly enjoy the frequent use of triple and quadruple negatives!   I *hope* my explanations of similar systems to our newbies doesn't sound like that, but based on the glazed looks, it probably does.

     Brett

Depends on the newbie Brett!
HAHAHAH......more maniacal laughter...   

[Carl Cisneros]

Dale

glad to be of service. don't lose that.................

Brett;

Thought you might like it.
And yes, the young airmen we were instructing looked like deer in headlights.  LOL

Then the fun really began...............

Carl

[Ken Culbertson]

Here it is Ken and Sean===============

We actually did this originally in 1971.

I have a question.  What if it is an older INS system that can't remember where it hasn't been and is not sure where it was?
Maybe I need to switch to GPS.

Ken

[Brett Buck]

Dale

glad to be of service. don't lose that.................

Brett;

Thought you might like it.
And yes, the young airmen we were instructing looked like deer in headlights.  LOL

Then the fun really began...............

Carl

      The basic idea is so simple, I don't see why it is so hard to understand or explain. But it does seem to throw people or cause frequently brain-locks.

       Brett

[Tim Wescott]

... "willingness to travel to austere environments" ...

Why do they do that?  Do they really want someone dumb enough that they can't decode that?