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Author: Subject: The Short Questions Thread (4)
mr_bovinejony
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[*] posted on 18-3-2024 at 16:41


Nope but I do love that book lol. Theres another shortter one called the recent advances in phosgene chemistry, these are the only two books I have on phosgene
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mr_bovinejony
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[*] posted on 18-3-2024 at 16:42


Nope but I do love that book lol. Theres another shortter one called the recent advances in phosgene chemistry, these are the only two books I have on phosgene
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bnull
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[*] posted on 18-3-2024 at 17:00


What about "A mild and efficient method for the preparation of acyl azides from carboxylic acids using triphosgene" (Tetrahedron Letters 43 (2002) 1345–1346)? Edit: No, it isn't.

Do you remember what was the reaction?

[Edited on 19-3-2024 by bnull]




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yobbo II
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[*] posted on 27-3-2024 at 13:58


Could someone tell me what is meant by the feature on these true RMS meters?

AC + DC Measurement


The meters are at this link>

https://www.aliexpress.com/item/1005003126913969.html?src=go...
It is circled on the picture

TIA,
Yob

acdc.gif - 90kB

[Edited on 27-3-2024 by yobbo II]
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B(a)P
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[*] posted on 27-3-2024 at 14:54


Quote: Originally posted by yobbo II  
Could someone tell me what is meant by the feature on these true RMS meters?

AC + DC Measurement


The meters are at this link>

https://www.aliexpress.com/item/1005003126913969.html?src=go...
It is circled on the picture

TIA,
Yob



[Edited on 27-3-2024 by yobbo II]


eevblog is a great resource for electronics questions. Check out this thread.
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bnull
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[*] posted on 27-3-2024 at 15:04


Quote: Originally posted by yobbo II  
Could someone tell me what is meant by the feature on these true RMS meters?

AC + DC Measurement

When the voltage has a component AC and a component DC (DC offset), ordinary meters measure either the AC component or the DC component but not both at the same time. The AC+DC meter measures both and outputs this:
$$V_{RMS_{(AC+DC)}}=\sqrt{V_{DC}^2+V_{RMS_{AC}}^2}.$$
It's for those times when you want to know the power dissipation in a resistor, for example.

Edit: Victim of ninja attack because of a typo in LaTeX. You won't get me next time, B(a)P, mark my words. :D

[Edited on 27-3-2024 by bnull]




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yobbo II
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[*] posted on 28-3-2024 at 05:43



Thanks you folks.
Yob
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wg48temp9
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[*] posted on 4-4-2024 at 18:56


Quote: Originally posted by bnull  
Quote: Originally posted by yobbo II  
Could someone tell me what is meant by the feature on these true RMS meters?

AC + DC Measurement

When the voltage has a component AC and a component DC (DC offset), ordinary meters measure either the AC component or the DC component but not both at the same time. The AC+DC meter measures both and outputs this:
$$V_{RMS_{(AC+DC)}}=\sqrt{V_{DC}^2+V_{RMS_{AC}}^2}.$$


If you mean it performs that sum then that is incorrect. A true rms meter simple calculates the rms of the signal be it AC, DC or a combination of both.

Notice the first multimeter (UT8802) is not a true rms meter and has modes for DC and modes for AC. In AC mode it measures the mean rectified signal then increases it by 0.11 assuming its a sine wave. The ratio of the rms to the mean of rectified sine wave is 1.11. If you measured the rms of a + and - square wave it would give reading 0.11 too large.

The true rms multimeters (UT8803, I don't know about UT8804) do not have different ranges for AC and DC, its not needed because they calculate the true rms.

Modern true reading multimeters sample the signal and calculate the rms from the samples. The expensive UT8805 even provides different functions it can perform on the samples.


[Edited on 4/5/2024 by wg48temp9]




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bnull
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[*] posted on 5-4-2024 at 01:47


Quote: Originally posted by wg48temp9  
If you mean it performs that sum then that is incorrect. A true rms meter simple calculates the rms of the signal be it AC, DC or a combination of both.

"AC+DC measurement: Measure signals with AC and DC components (including various waveforms)
Ordinary multimeters can only measure pure AC/DC signals. If the measured AC signal is mixed with the DC signal, the AC signal reading is meaningless. For Uni-Trend’s multimeters with AC+DC function, the AC and DC components are measured together." (https://meters.uni-trend.com/faqs/acdc-measurement/)

"AC and DC are components of a complex signal.
AC Voltage means RMS Voltage for AC component (effective Voltage of alternating current).
DC Voltage means Voltage for DC component (constant Voltage offset).

Both components produce power dissipation on the applied load.
So, you're needs to sum them together in order to get effective Voltage for a total dissipated power.

AC+DC Voltage = sqrt([AC RMS Voltage]^2 + [DC Voltage]^2)" (https://www.eevblog.com/forum/beginners/can-someone-explain-...)

"If you are expecting to include the DC component, but the meter is AC coupled, the results can be dramatically wrong. As a side note, if you need to measure a small AC signal riding on a large DC offset but your meter doesn’t provide AC + DC directly, you can measure the AC component using AC coupling and measure the DC component separately. Then add the two using rms addition:
AC + DC =sqrt((ACrms)2+DC2)" (Make Better AC RMS Measurements with your Digital Multimeter. Application note, Keysight Technologies, 2018. There's a bloody typo in the formula that they never bothered to fix.)

True-RMS Measurement Pt.1: AC vs. AC+DC. "Roger demonstrates the difference between so called "True-RMS" (only AC) and "True-RMS AC+DC" multimeters and a simple AC-averaging multimeter." (https://www.youtube.com/watch?v=LZEie3nAo1E) meter1.jpg - 85kB

Quote: Originally posted by wg48temp9  
I don't know about UT8804

That's the one in question:

meter.jpg - 154kB

[Edited on 5-4-2024 by bnull]




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[*] posted on 7-4-2024 at 01:12


I have now had time to view the details of UT8804.

Below is a snip of the selection switch for the UT8804:

rms04Screenshot 2024-04-07 072929.jpg - 75kB

I think the symbol next to all the current ranges is intended to indicate mixed AC and DC signals which are measured true rms ie calculating the rms from a set of samples of the signal DC coupled. I think some people are calling this "AC + DC" mode.

On the voltage range there or two different symbols one usually indicates AC and the other DC. I would expect the AC range to be AC coupled and measures the RMS of the AC component. Does the DC position indicate average or rms ?

The UT8803 only uses the mixed symbol that the current ranges of the UT8804 uses. Meaning it only measures true rms DC coupled

I suspect the tick in AC+DC column for the 04 refers to the two voltage ranges, AC range and DC range that the 03 does not have.

I am very interested in these meters as they both have a usb interface. I expect to purchase the 03. If I want to measure the AC component of a mixed AC and DC voltage l I will add a series capacitor to one of the test leads.



[Edited on 4/7/2024 by wg48temp9]




I am wg48 but not on my usual pc hence the temp handle.
Thank goodness for Fleming and the fungi.
Old codger' lives matters, wear a mask and help save them.
Be aware of demagoguery, keep your frontal lobes fully engaged.
I don't know who invented mRNA vaccines but they should get a fancy medal and I hope they made a shed load of money from it.
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bnull
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[*] posted on 7-4-2024 at 06:47


Quote: Originally posted by wg48temp9  
I think the symbol next to all the current ranges is intended to indicate mixed AC and DC signals which are measured true rms ie calculating the rms from a set of samples of the signal DC coupled. I think some people are calling this "AC + DC" mode.

On the voltage range there or two different symbols one usually indicates AC and the other DC. I would expect the AC range to be AC coupled and measures the RMS of the AC component. Does the DC position indicate average or rms ?

The UT8803 only uses the mixed symbol that the current ranges of the UT8804 uses. Meaning it only measures true rms DC coupled

I suspect the tick in AC+DC column for the 04 refers to the two voltage ranges, AC range and DC range that the 03 does not have.

I am very interested in these meters as they both have a usb interface. I expect to purchase the 03. If I want to measure the AC component of a mixed AC and DC voltage l I will add a series capacitor to one of the test leads.
[Edited on 4/7/2024 by wg48temp9]


Read the UT8804E manual (http://unitrend.oss-cn-hongkong.aliyuncs.com/upload/file/202...), starting on page 9.




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mr_bovinejony
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[*] posted on 25-4-2024 at 18:05


Will clemmensen reduce 3 bromo benzaldehyde to 3 bromo toluene or will it remove the bromine?
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[*] posted on 26-4-2024 at 05:32


Quote: Originally posted by mr_bovinejony  
Will clemmensen reduce 3 bromo benzaldehyde to 3 bromo toluene or will it remove the bromine?

Not sure but I do know that this method will reduce the aldehyde without affecting the bromine:

https://pubs.acs.org/doi/pdf/10.1021/ja01860a035




Quote: Originally posted by bnull  
you can always buy new equipment but can't buy new fingers.
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mr_bovinejony
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[*] posted on 26-4-2024 at 14:05


Very cool, now just gotta find some hydantion or hippuric acid
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[*] posted on 26-4-2024 at 21:53


Hydantoin is easily prepared from glycine and urea: https://www.sciencemadness.org/whisper/viewthread.php?tid=15...



Wroom wroom
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mr_bovinejony
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[*] posted on 27-4-2024 at 02:42


Awesome, though not a fan of the 50 hour reflux mentioned in the paper when they reduce o-chlorobenzylhydantoin. Guess this will be a last resort option
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[*] posted on 24-5-2024 at 00:56


Hi folks!

I have few short questions regarding stellar nucleosynthesis. Sorry if this don't belong here, but I don't want to start new thread because of few stupid questions.

1. Stellar nucleosynthesis ends with 56Ni. I read that it could continue further, because alpha process is exothermic up to 100Sn. But because of high temperature and pressure rate of photodisintegration is so high that it prevent further process. I get how pressure affects it (atoms are more densly pact, higher chance of collision with photon), but how temperature affects it? Photons aren't affected by temperature.

2. https://en.m.wikipedia.org/wiki/Carbon-burning_process

I don't get why isn't reaction 4 favored. Why excited 24Mg release hellium, hydrogen or neutron rather than photon? Isn't braking atom more difficult than releasing photon? Same thing for 32S in oxygen burning.

3. Why neon in neon burning doesn't fuse with another neon like carbon/oxygen in carbon/oxygen burning?

4. Is there a way how to calculate activation energy for nuclear fussion?

5. 4He is most commonly emited atomic nucleus. It makes sense because it's small and highly energiticaly favorable. But why isn't emission of 12C or 16O also common? These nuclei are also energetically favorable, 16O is doubly magic (like 4He).
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