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The 0-3 Amp meter looks interesting, but I would prefer to find one for $5 at a ham radio swap meet. Or ask a local ham to refer you to an old-timer that used to build their own equipment and might have a well stocked junk box.
Generating 3 amps of RF and running it around to the meter movement doesn't sound appealing. And 1 amp is down at the low resolution end of the scale. Removing the thermocouple and placing it next to the0..02 or whatever ohm resistor and adding an amplifier to make a more reasonable current full scale makes more sense. Be sure to carefully mark the RF terminals and output voltage terminals carefully.
John
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On 8/31/2022 11:23 AM, Jeff Green wrote: I'm not sure if anyone will find these useful, but they might.
Some of these have built in thermocouples to measure RF current. I don't know enough to know what the upper frequency of operation might be.
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I have been wondering if it’s possible to make an RF ammeter from nichrome wire and measure the IR radiation to measure the heat caused by the RF current. A DC substitution would allow the RF current to be determined. Similar to what HP & Boonton did, but not using a thermocouple. There are a few possible techniques for measuring the temperature without actually being in contact with the nichrome wire
1) Thermopile which I believe are used in cheap (<$20 USD) IR thermometers?
2) Photodiode.? The issue here is that the peak emission of a hot wire at 100 deg C is 7.8 um, which is much longer than any photodiode technology I am aware of, but there will still be emissions at shorter wavelengths.?
Silicon has the advantage of being very cheap, but the cutoff wavelength is quite short (around 1.1 um). Germanium is less readily available, but works to longer wavelengths??The dark current is higher too. InGaAs devices work to around 2.6 um. These are usually cooled, and are unlikely to be cheap.?
3) CCD, as used in thermal imaging cameras, I believe they are silicon?
Dave?
-- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@...Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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How do you vary the size of the quantum hole?
Ken g8beq
On 01/09/2022 12:11, Jeff Green wrote:
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In a prior life I was a chemical
engineer....
?
This is getting pretty theoretical.
Quantum Dot "Solar Cells" can be tuned
for different wavelengths by varying the size of the quantum
"hole,"
AKA "Quantum Well."
?
?
?
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Vary the size of the quantum hole? You call Heisenberg. Or maybe Schr?dinger, I forgot.
?
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Sigma Aldrich sell quantum dots in
various sizes, mostly in the optical range though.
CdSe/ZnS core-shell type quantum dots,
stabilized with octadecylamine ligands, fluorescence λem?540?nm,
solid
10 mg for a mere ?330.? Plus VAT
Cheap at twice the price.....
Neil G4DBN
On 01/09/2022 16:37, Wilko Bulte wrote:
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Vary the size of the quantum hole? You call Heisenberg. Or maybe Schr?dinger, I forgot.
?
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The sensors that Barry Chambers is
using for 30 THz comms testing are relatively low cost Melexis
single pixel IR bolometers.? The 90614 is good enough to detect
the thermal radiation from the Moon and is calibrated for
temperatures from -170 to +380 °C and compensated for a wide range
of device temperatures.? It has a resolution of 0.02 °C and could
probably be used to monitor the temperature of an 0603 or 0402
load resistor.? Might need a germanium or similar longwave IR lens
if the load resistor is to small to fill the sensor active area.
Other models have onboard DSP filtering
and multi-zone sensors.? Base models are around ?30 in 1-off.
--
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Could you place nichrome wire against the bulb of an alcohol thermometer?
The alcohol should have no appreciable effect on inductance.
Yes, in principle. although only a small area would be in contact with the glass. The other problem is that its not possible to easily get the data in a electronic (digital or analog) format.?
I have just ordered a couple of cheap IR photodiodes from RS
I bought one to try, and another to see it was possible to use it as an avalanche photodiode (APD). Not that I particularly need an APD, but I wondered if it might work in avalanche?mode. They were cheap enough to not worry about the cost.?
-- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@...Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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Even if you could get accurate measurements with the limited contact area, you would still be faced with the slow response time of a glass thermometer. Makes adjustments difficult.
I like the idea of a fixed gain amplifier and diode detector directly measuring the voltage across the 0.02 or whatever ohm resistor.
John
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On 9/1/2022 3:33 PM, Jeff Green wrote: Could you place nichrome wire against the bulb of an alcohol thermometer?
The alcohol should have no appreciable effect on inductance.
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I’d use a current transformer, with a suitable detector. The detector could be a simple rectifier, or a nice logarithmic power meter, such as one based on an AD8307.
The article below includes the design of a CT that produces about 5 V/A into 50 ohms from 0.2-170 MHz, -3 dB.
Gary NA6O?
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Following this thread with interest. I would probably try a low value chip resistor epoxied to a thermistor. The resistor would be in series with the center lead of the coax. With a little thermal isolation. I don't think a resistor in series in the RF circuit would be significantly more lossy than current transformers or other methods of measuring RF current. Maybe even better than other methods.? The advantage of the chip resistor would be frequency range and true RMS readings. You could put a second resistor/thermistor that you control a D.C. current into and make a bridge if you wanted to be really accurate. Otherwise just let a microprocessor do a curve fit on a single resistor/thermistor against another ambient temperature reading. Interesting about the indirect temperature measurement ideas. Here is a link from a quick search. I'm sure there are other, maybe better, choices with a little more searching. There are far infrared sensors with digital interfaces (I2C), too.
The wavelengths used for non-contact temperature measurement seem to be around the?8 ?m to 14 ?m range.
Tom, wb6b
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On Thu, Sep 1, 2022 at 04:33 PM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
I have just ordered a couple of cheap IR photodiodes from RS
?
?
It would be interesting to try these IR photodiodes with a very small lightbulb as the current sensor, where the measured current just brings the filament to the dull red glowing range. Wonder if the increasing resistance with temperature of the filament would be an issue. Possibility causing the filament output to go from barely readable (under range) to bright glow (and over range) over a small current range. Or if operating at the "low" (barely glowing) filament temperatures would mitigate that. Sounds interesting to experiment with.? Tom, wb6b
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On Fri, 2 Sep 2022 at 00:40, John Kolb < jlkolb@...> wrote:
Even if you could get accurate measurements with the limited contact
area, you would still be faced with the slow response time of a glass
thermometer.? Makes adjustments difficult.
Agreed
I like the idea of a fixed gain amplifier and diode detector directly
measuring the voltage across the 0.02 or whatever ohm resistor.
That requires making and calibrating an RF volt meter. I don’t know the what sort of accuracy one could achieve with that, but I don’t have any obvious ways of checking that. If that resistor was 10 m ohm, which was the sort of value I was hoping to use, a 50 ohm power meter would cause negligible loading. But RF lower measurements are tricky, and achieving a 2% uncertainty is tricky. Neither my RF power meter no the 10 MHz to 18 GHz sensors are calibrated. At least a thermal method can be calibrated with DC substitution. I suspect that my uncertainty of a thermal method would be lower than I achieve with an RF volt meter.?
I am interested in making the overall uncertainty of Q measurements as low as possible - not because I have a need for a low uncertainty, but because it would be interesting to do the best job possible.
John
Dave? -- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@...Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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Pearson and Ion Physics make CT’s suitable for RF applications. Some have a rise time as short as 2ns (=>500MHz). Some are expensive though. ? See Pearson’s website at ? Not sure if Ion Physics is still in business. ? I have a couple of Pearson units and they are very well make. ? Cheers, George VK2KGG ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Tom, wb6b
Sent: Friday, 2 September 2022 12:08 PM
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] RF Current meters ? Following this thread with interest.
I would probably try a low value chip resistor epoxied to a thermistor. The resistor would be in series with the center lead of the coax. With a little thermal isolation. I don't think a resistor in series in the RF circuit would be significantly more lossy than current transformers or other methods of measuring RF current. Maybe even better than other methods.?
The advantage of the chip resistor would be frequency range and true RMS readings.
You could put a second resistor/thermistor that you control a D.C. current into and make a bridge if you wanted to be really accurate. Otherwise just let a microprocessor do a curve fit on a single resistor/thermistor against another ambient temperature reading.
Interesting about the indirect temperature measurement ideas. Here is a link from a quick search. I'm sure there are other, maybe better, choices with a little more searching. There are far infrared sensors with digital interfaces (I2C), too.
The wavelengths used for non-contact temperature measurement seem to be around the?8 ?m to 14 ?m range.
Tom, wb6b
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On Fri, 2 Sept 2022 at 03:46, Tom, wb6b < wb6b@...> wrote: On Thu, Sep 1, 2022 at 04:33 PM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
I have just ordered a couple of cheap IR photodiodes from RS
?
?
It would be interesting to try these IR photodiodes with a very small lightbulb as the current sensor, where the measured current just brings the filament to the dull red glowing range. Wonder if the increasing resistance with temperature of the filament would be an issue. Possibility causing the filament output to go from barely readable (under range) to bright glow (and over range) over a small current range. Or if operating at the "low" (barely glowing) filament temperatures would mitigate that. Sounds interesting to experiment with.?
Tom, wb6b
I would not expect it to be necessary for the bult to be visible to the human eye before an IR photodiode could detect it. But I don't know. The issue I see with bulbs is their inductance. The other thing is I want to use a step-down transformer to drive the resistor. That probably means having one turn on the secondary. That one-turn could be a piece of nichrome. It is available as a strip, which would reduce the inductance compare to a cylindrical wire.
I use nichrome wire to cut foam inserts for VNA calibration kits my company sells. I use a fairly thick wire, and put 5.5 A in it, so it glows red hot. But I will be able to put the photodiode near that and see at what current I can detect it. I would hope the IR could be detected long before I can see the wire getting hot, but maybe not. At least it costs virtually nothing to try. I have a high-resistance meter which will read pA (maybe even fA), so knocking something up quick should be easy.
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On Fri, Sep 2, 2022 at 03:34 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
I use nichrome wire to cut foam inserts for VNA calibration kits my company sells. I use a fairly thick wire, and put 5.5 A in it, so it glows red hot. But I will be able to put the photodiode near that and see at what current I can detect it. I would hope the IR could be detected long before I can see the wire getting hot, but maybe not. At least it costs virtually nothing to try. I have a high-resistance meter which will read pA (maybe even fA), so knocking something up quick should be easy.
This will be very interesting to find out at what point the temperature of the wire gets to the point that it can be detected by a near infrared diode. Definitely has a possibility of being good low cost method. While I was thinking about light bulbs because the filament may be thermally isolated inside the bulb, the possible inductance issue is well taken. Plus nichrome wire, if ?remember correctly, has a fairly low change in resistance with temperature, unlike the light bulb.? Will be interested in watching for your results. And if the temperature that the nichrome wire may need to operate at is fairly high, this may lessen the need to compensate for ambient temperature. Tom, wb6b
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On Fri, 2 Sep 2022 at 03:08, Tom, wb6b < wb6b@...> wrote: Following this thread with interest.
I would probably try a low value chip resistor epoxied to a thermistor. The resistor would be in series with the center lead of the coax. With a little thermal isolation. I don't think a resistor in series in the RF circuit would be significantly more lossy than current transformers or other methods of measuring RF current. Maybe even better than other methods.? I am personally interested in doing this in a low impedance circuit. That probably means having a transformer with a single turn on the secondary. A bit of nichrome wire as the secondary would be convenient if it could be the current sense too.
The advantage of the chip resistor would be frequency range and true RMS readings.
I hope not! RMS power is a useless parameter . You can compute it analytically, but it is pretty meaningless. The mean power is what is relevant, as that causes the same heating as DC would.?
You could put a second resistor/thermistor that you control a D.C. current into and make a bridge if you wanted to be really accurate. Otherwise just let a microprocessor do a curve fit on a single resistor/thermistor against another ambient temperature reading.
Interesting about the indirect temperature measurement ideas. Here is a link from a quick search. I'm sure there are other, maybe better, choices with a little more searching. There are far infrared sensors with digital interfaces (I2C), too.
The wavelengths used for non-contact temperature measurement seem to be around the?8 ?m to 14 ?m range.
Yes, that does seem to be the case. The peak of the emission curve
Assuming this calculator is right?
the peak emission vs temperature are
20 °C ?= 9.885 um 100 °C = 7.766 um 500 °C = 3.748 um 1000 °C = ?2.276 um 2447 °C = 900 nm (peak sensitivity of IR LED I ordered)
It’s clear that a black body resistor or nichrome wire would not have its peak radiation anywhere near the peak sensitivity of the silicon photodiode, but it might be usable. For a ?1 each, with free next-day shipping, it is worth a try.
Tom, wb6b
Dave _._,_._,_
-- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@...Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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One technique , I think it was an HP RF power meter. Used a thermistor in a bridge configuration, which had a bias supply to set the thermistor to a particular resistance. When the RF was applied, it unbalanced the bridge. The bias, was (automatically) controlled, and reduced until the bridge was in balance. And this control loop indicated the applied RF power. ? Rodger Bean ?
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From: [email protected] <[email protected]> On Behalf Of Tom, wb6b
Sent: Friday, 2 September 2022 21:45
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] RF Current meters? On Fri, Sep 2, 2022 at 03:34 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote: I use nichrome wire to cut foam inserts for VNA calibration kits my company sells. I use a fairly thick wire, and put 5.5 A in it, so it glows red hot. But I will be able to put the photodiode near that and see at what current I can detect it. I would hope the IR could be detected long before I can see the wire getting hot, but maybe not. At least it costs virtually nothing to try. I have a high-resistance meter which will read pA (maybe even fA), so knocking something up quick should be easy.
This will be very interesting to find out at what point the temperature of the wire gets to the point that it can be detected by a near infrared diode. Definitely has a possibility of being good low cost method. While I was thinking about light bulbs because the filament may be thermally isolated inside the bulb, the possible inductance issue is well taken. Plus nichrome wire, if ?remember correctly, has a fairly low change in resistance with temperature, unlike the light bulb.?
Will be interested in watching for your results. And if the temperature that the nichrome wire may need to operate at is fairly high, this may lessen the need to compensate for ambient temperature.
Tom, wb6b
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On Fri, Sep 2, 2022 at 05:29 AM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
I hope not! RMS power is a useless parameter . You can compute it analytically, but it is pretty meaningless. The mean power is what is relevant, as that causes the same heating as DC would.?
I think the measured amperage would be RMS, by virtue of measuring the temperature of the resistor. Guided by the title of thread, was only referring to current.? Interesting calculator for temperature to peak wavelength. I've had some trying out some common temperature values. The sample curves in the description are nice for getting a feel for how far the hot body spectrum would extend into the near infrared.? Tom, wb6b
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Those bolometer chips work from well
below zero (C or F) to a few hundred. Getting the environment for
the sensing element to be consistent and stable over the
measurement period is always going to be a challenge, but if you
run DC and RF at the same time and run with the sensor at a
constant temperature in a temperature-controlled housing, it ought
to be possible to remove environmental influences simply by
servoing the DC with a PID loop to keep the temperature of the
element constant.? Ideally it would be in a vacuum so the only
heat loss was via radiation into an environment which acts as a
black body at a fixed (lower) temperature, and by conduction
through the mount and connections, but a sealed enclosure with air
would probably be OK given the enclosure is at a fixed temp and
the servo drives the sensor to the same fixed temp. It's
self-calibrating as well of course, only requiring precise
measurement of the DC current and compensation for frequency
response.
Using a contact thermistor would reduce
the sensitivity by increasing the thermal mass of the sensor, but
perhaps not by more than half.? Usually you have to compensate for
the heating effect of sensing current in the thermistor, but if
the sensor is held at a constant temperature, heating from the
sensing current of the thermistor would be constant once the loop
settled.? Also the thermistor could be sampled with a very low
duty cycle A/D converter to reduce the heating to imperceptible
levels.? Two 0402 SMD chips with short foil connections and
thermal glue in a cutout on a PCB and enclosed in a black-painted
milled aluminium enclosure with a mosfet heater and temp control
chip perhaps?
DC injection would need an isolated
supply and wideband conical chokes.? Hmmmm. Sounds like a whole
lot of fun.?
Neil
On 02/09/2022 13:29, Dr. David Kirkby,
Kirkby Microwave Ltd wrote:
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On Fri, 2 Sep 2022 at 03:08, Tom, wb6b < wb6b@...>
wrote:
Following
this thread with interest.
I would probably try a low value chip resistor epoxied to a
thermistor. The resistor would be in series with the center
lead of the coax. With a little thermal isolation. I don't
think a resistor in series in the RF circuit would be
significantly more lossy than current transformers or other
methods of measuring RF current. Maybe even better than other
methods.?
I am personally interested in doing this in a
low impedance circuit. That probably means having a
transformer with a single turn on the secondary. A bit of
nichrome wire as the secondary would be convenient if it could
be the current sense too.
The advantage of the chip resistor would be frequency range
and true RMS readings.
I hope not! RMS power is a useless parameter .
You can compute it analytically, but it is pretty meaningless.
The mean power is what is relevant, as that causes the same
heating as DC would.?
You could put a second resistor/thermistor that you control a
D.C. current into and make a bridge if you wanted to be really
accurate. Otherwise just let a microprocessor do a curve fit
on a single resistor/thermistor against another ambient
temperature reading.
Interesting about the indirect temperature measurement ideas.
Here is a link from a quick search. I'm sure there are other,
maybe better, choices with a little more searching. There are
far infrared sensors with digital interfaces (I2C), too.
The wavelengths used for non-contact temperature
measurement seem to be around the?8 ?m to 14 ?m range.
Yes, that does seem to be the case. The peak of
the emission curve
Assuming this calculator is right?
the peak emission vs temperature are
20 °C ?= 9.885 um
100 °C = 7.766 um
500 °C = 3.748 um
1000 °C = ?2.276 um
2447 °C = 900 nm (peak sensitivity of IR LED
I ordered)
It’s clear that a black body resistor or
nichrome wire would not have its peak radiation anywhere
near the peak sensitivity of the silicon photodiode, but
it might be usable. For a ?1 each, with free next-day
shipping, it is worth a try.
Tom, wb6b
Dave
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I'd like to suggest another option. I have some Platinum RTD temperature sensors bought for another project. They are very stable and accurate as temperature sensors and relatively cheap. They are also very small - small enough to be used as an RF load in a BNC or SMA fixture, with bandwidth extending, possibly, to the low GHz region. Mine have leads; but they are available in surface mount packages. 100 Ohms is the most commonly supplied resistance; so 2 in parallel could make a nice 50 Ohm load.? A third sensor could serve as a reference in a bridge circuit. Alteratively, one might preheat to a known temperature with DC and measure the DC power drop required to achieve the same temperature with RF applied. Other readout options also exist, including lock-in if the RF power can be modulated.
Stephen Menasian
Stephen Menasian
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John Kolb
Dr. David Kirkby, Kirkby Microwave Ltd