Recent Posts

1

Beginners / Re: Switching a 3KW (240V) immersion heater: Solid state or mechanical relays?

« Last post by 5U4GB on Today at 10:27:19 am »

driving a higher-power contactor like the Finder 65's that people have recommended,

A followup question about this, the usual-suspect electrical suppliers, meaning ones who provide the necessary SDOC, can only provide the 2xNO with a minimum order quantity of five while they have 1xNO, 1xNC in stock in single-unit quantities.  If I source it myself from Farnell or whatever it won't come with an SDOC.  Given that I'm only switching a pure resistive load that heats water rather than, say, turning limb-removing power machinery off, so even if contact welding occurs it's no big deal, is it worth going to the 2xNO supplied-by-user to switch active+neutral or is it good enough to use the 1xNO with SDOC to switch active only?

Also, am I overthinking this? :-).

2

Beginners / Re: Power supply output transistors

« Last post by xavier60 on Today at 10:26:31 am »

This project happened near to 6 years ago.
This is a version I had drawn that's simply driven by Pots, for anyone wanting to experiment with it.
There may be no simple way of implementing a simple linear regulator that also works properly.
The other option is the BJT design I used in a 5A PSU which may be able to be beefed up with more output transistors.
How many, I can't say for certain, at least 4 with a pre-regulator.
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664

3

Repair / TEK 475A VOLTS/DIV compensation problem

« Last post by fabio.deangelis on Today at 10:25:25 am »

Hello EVVBloggers,
I have recently restored an old TEK 475A oscilloscope bought on eBay for a few Euro. The main problem was a faulty high voltage multiplier and a bad electrolytic capacitor on the +15 volt rail. Another issue was the “blocked” fan cooler that I have attempted to restore by replacing a faulty U1690 with four transistors and grease the motor. The fix apparently worked but unfortunately the fan motor did not start at power on all times. I had to make an agonizing decision, replacing the sophisticated Tek fan motor assembly with a small computer fan, attached to the +15 volt with a resistor ☹
The scope is now working very well in all functions but a weird issue in the VOLT/DIV compensation. I am unable to compromise the compensation among the 0.1, 0.2 and 0.5 Volt positions. Once I compensate the 0.1 position (C32, C33 if I remember correctly), then I got a bad image (under compensated) on 0.2 and 0.5 positions. If I re-adjust C32,C33 for a flat square image on those positions then I got a bed image (over compensated) on 0.1 volt position. The problem is present on both channels, even if it is more evident on CH1. I believe I have successfully performed the vertical calibration steps present before the VOLT/DIV compensation adjustment. I did a test by replacing the “compensator unit” (C32 C3) taken from another 475 , but the result is unchanged. Note that I have thoroughly cleaned the attenuator switches, which appear to work well.
Any clue what could be the issue here ?

4

Repair / Re: Capacitor has different readings if stored upside down

« Last post by TERRA Operative on Today at 10:23:47 am »

Turn them back over so they are sitting upright for a while and test again to see what they say.

5

Microcontrollers / Re: Signal filtering - Could this work ?

« Last post by gf on Today at 10:21:18 am »

The CIC filter already does the moving average ?

A CIC filter is just a particular way to implement a 1st order or higher¹⁾ order moving average filter. A CIC structure is particularly useful in combination with down- or up-sampling.

I think that the first that have to do it's take long raw measurement from field and then find out best math (filters/DSP/etc), that will solve your problem (with something like MATCAD). And only after this start to implement algorithms in firmware.

  I wanted to suggest the same. Collect at least a few minutes of data (or better an hour - even that's only 1.44 million samples), and analyze it first.

And try to specify requirements like
- What is the desired accuracy / uncertainty?
- Do you want real-time display for instantaneous fill level and instantaneous weight loss per second?
- How much settling time / delay are you willing to accept?


1) An N-th order moving average filter is a concatenation of N equal 1st order moving average filters. Just send the output of the 1st stage into the next stage, and so on. It's also called sinc^N filter, which refers to the shape of the magnitude of the resulting frequency response.

6

Test Equipment / Re: Test Equipment Anonymous (TEA) group therapy thread

« Last post by TERRA Operative on Today at 10:19:21 am »

Ah, found it here:

https://www.eevblog.com/forum/testgear/replacement-knobs-feet-and-fittings-for-test-equipment/msg2350938/#msg2350938

7

General Technical Chat / Re: ultra sonic transducers

« Last post by PlainName on Today at 10:15:12 am »

Sounds like you need an evening rock festival to keep him up past his bedtime.

Depending on where you live, that sort of disturbance (the dogs) would warrant a visit from the local authority, hopefully resulting in a Notice:

https://www.middevon.gov.uk/residents/dogs/dog-barking/

8

Beginners / Re: buying a oscilloscoop

« Last post by scroeffie on Today at 10:13:45 am »

back again have 2 questions .are these any good for me as a beginner   https://www.eleshop.nl/owon-oscilloscope-probes-2kv.html

second question we think we have found the problem of my ibm psu these 2 optos are not working corectly anymore and they are very old like 30+ years old
the monitor also has been working like around the clock in a factory crt monitor is a ibm 8514 there is no schematic that i can find ,other than this small problem \
i already did a full recap some caps where dead .
if any one has a schematic or knows where what kind of replacement i could buy please let me know     

9

General Technical Chat / Re: new propellantless drive company

« Last post by iMo on Today at 10:12:58 am »

I had a quick look at the patent, and frankly the patent clerk AlbertE would laugh.
In the patent they state the stuff works in an enclosed system. So you have got something generatig a force inside a closed box and it should propell somewhere? That is against the fundamental laws of physics, imho.
They should apply for the Nobel prize as well..

10

Repair / Re: Precision Standards AC-DC Differential Voltmeter 360A - manual

« Last post by factory on Today at 10:10:48 am »

Does it seem to work?  I wonder if you can get by without the manual.

Give it a visual inspection inside before trying it, to make sure there are no burnt parts, or any of those leaking wet tantalum capacitors that were commonly used in some 60s & 70s test gear.

David