Recent Posts

1

Test Equipment / Re: Fun With Low Leakage/Bias Current: Femtompere, Electrometer, Keithley 617

« Last post by Alex Nikitin on Today at 02:24:42 pm »

After put back the original BNC connector, I recorded the offset. Is it normal or not?  thanks

If that is the drift when switching on from cold, it might be normal. According to the manual, the warm up time to rated accuracy is 2 hours. There are two trimmers on the input board, one to adjust the DC offset (in the Voltage measuring mode) and the second is to compensate the input current (in the Current measuring mode), so it can be adjusted to zero. Both are not easy adjustments, mostly because you need to keep the top cover on to get the temperature stable and correct, than open the cover (thus upsetting the thermal equilibrium) to do the adjustments, only to close it quickly and see if you hit the spot after the temperature settles again  . Both the offset and the input current will drift noticeably when you open/close the cover however by several iterations it is possible to get a reasonable result.

Cheers

Alex

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Beginners / Re: What function generator, that does a bit more than just a simple signal

« Last post by radiolistener on Today at 02:23:18 pm »

Have you used the programming feature? The manual is not so good to explain things here. Also i wonder if there are limitations when using some more complex function on one channel, for example using sweep or FM/AM/... : The other channel can be used what ever you want to do with it? Is it possible to use AM/FM/... on one channel, and sweep (with fm) on the other?

If you're talking about JDS2800, I don't have it so I can't say. I have PSG9080.

Both are manufactured by the same manufacturer and has similar display interface, so I think my tool designed for PSG9080 can be compatible with it.

Regarding to PSG9080, it has nice front panel with large contrast display. The performance is comparable with the same class generators like FY6800, may be a little bit less noise but harmonics may be a little bit higher. I would not expect something special, this is just a signal generator. It has sweep and modulation, but these functions are limited and has not a good quality. If you want some more functions or better quality sweep and modulation, it's better to look for something more higher class. Like Siglent SDG2048X.

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Projects, Designs, and Technical Stuff / Re: Vacuum Fluorescent Display Driver

« Last post by bostonman on Today at 02:11:46 pm »

I thought the DC-DC output AC to the filaments?

At the time I only had schematics handy and saw it's a "DC-DC" convertor, so I assumed it was DC out, however, I should have included that I measured the AC as well, it was approximately 600mV; but I measured this with respect to ground and maybe needed to measure across.

The datasheet specifies pins 5 and 7 are AC, but doesn't give a voltage. The schematic shows FL1 and FL2 are on pins 4 and 6, so that's a bit confusing.

Later today or tomorrow (hopefully) I'll take the steps you suggested. Usually I start with the obvious such as do I have voltage(s). My personal rule is first figure out what happened between when something worked and when it didn't. Since the only anomaly in that process was me replacing the chip, seems the obvious route is to start with soldering issues.

My other thought is the replacement IC takes more current and damaged the convertor. My somewhat focus is on the fact the display was working until I recycled power. As you suggested, a power up sequence failure, shorted pins, etc... so I'll look and report what I find.

Update: just for reference, this is the chip I ordered and installed    HV518PJ-G (DigiKey part number: HV518PJ-G-ND)

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PCB/EDA/CAD / Re: JLCPCB alters soldermask without any notice

« Last post by xvr on Today at 02:09:10 pm »

> They don't have strict rules for layer extension ".xxx" at JCL.

They have preferable naming (and it described on its site). If your files match it there is should be no problems. Otherwise they will do their best, but not always right

Very strange that they won't come back to you for approve 

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Projects, Designs, and Technical Stuff / Reactive Source Resonant Transformer

« Last post by Thor on Today at 02:02:10 pm »

This aims to make a resonant transformers output dominate in the parasitic Xc and the XL component of the output coils while reducing its ability to pass current in the R component of said coils.

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Projects, Designs, and Technical Stuff / Re: Accurate sine wave in terms of amplitude

« Last post by xvr on Today at 02:00:29 pm »

> One option is that: do not care.

Than use square waves. They can be considered as sinus with a lot of distortion.

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Test Equipment / Re: Cheap oscilloscope for checking mains power quality? Also logging equipment.

« Last post by Kean on Today at 01:51:54 pm »

I don't think an oscilloscope is the best solution based on your usage.  You want a power quality analyser with data logging.  Something that can also safely be left alone.

Maybe one of these.  https://powertronics.com/collections/single-phase-power-line-monitors

See these other related discussions
https://www.eevblog.com/forum/testgear/power-line-quality-monitor-that-does-not-cost-/
https://www.eevblog.com/forum/testgear/looking-for-a-cheap-but-good-single-phase-120v-power-line-glitch-logger/

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Projects, Designs, and Technical Stuff / Re: role of optocoupler for biasing drain of amplifiers

« Last post by xvr on Today at 01:51:44 pm »

In LTSpice schematic you again connect all 4 pins of MOSFET to different nets. I guess that one of them directly shot some MOSFET terminal to ground. There should not be.

As for 20V - power for your amplifier should be connected to terminal that in your schematic labeled 'After relay. 24V (ar)'. I don't know what relay was connected ant where, but definitely here should be connected just plain +20V. No any +24V from any relay should be used in final schematic.

In LTSpace change voltage of V1 to +20V and remove V3

> because this floating voltage is confusing. i am used to this of voltage where each node has exact voltage with respect to some reference.

Yes, but for flying voltage will be another reference - not common ground, as for all others.
If you want to see voltage on MOSFET gate set a probe to V(Gate)-V(Souce)

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Beginners / Re: LM324 Power Supply with variable voltage and current

« Last post by xavier60 on Today at 01:49:38 pm »

Do you mean that I need a separate winding on the transformer or another small transformer for the DVM and tap changer ?

Yes.

10

Test Equipment / Re: Fun With Low Leakage/Bias Current: Femtompere, Electrometer, Keithley 617

« Last post by BD1QMP on Today at 01:47:57 pm »

After put back the original BNC connector, I recorded the offset. Is it normal or not?  thanks