Recent Posts

1

Metrology / Current measurement with DMMs

« Last post by desert on Today at 12:00:57 pm »

I measured current with three DMMS: 1 pcs 34465A (6.5 with 7.5 current measurement accuracy) and 2 pcs 3458a (8.5).

A current source is used to deliver 4.5uA current, a DMM is in series with a 1M Ohm resistor. DMM “I” port is connected to current source output, DMM “LO” port is connected to 1M Ohm resistor, 1M Ohm resistor is connect to current source GND.

Auto range is used for current measurement. Only one DMM is connected for each time.
The current readings are (10uA range is used for both 34465A and 3458a):
34465A: 4.501uA
1st 3458a: 4.498uA
2nd 3458a: 4.500uA

Then I exchanged the connection of “I” and “LO” of DMMs (DMM “I” is connected to 1M Ohm resistor, DMM “LO” is connected to current source output).
The current readings are (10uA range is used for both 34465A and 3458a):
34465A: -4.500uA
1st 3458a: -4.284uA
2nd 3458a: -4.236uA

Why 3458a DMMs current reading have big changes while 34465A is relative stable?

After that, I connected current source directly with 1M Ohm resistor, no DMM is in series. I connected current source output to a DMM “I” port, “LO” port was left open. The recorded current readings are:
34465A: 11.9nA
1st 3458a: -13.6nA
2nd 3458a: -3nA

Are these readings reasonable? Why 4.5V voltage gives so big current error?

2

Test Equipment / Re: GW instek GOS-622g supply missing

« Last post by Kean on Today at 11:55:00 am »

This video seems to show a multi winding transformer connecting to J605.  It is hard to read in the video, but I think that is the label near the connector.



While he does open the scope up the video, there is not enough info shown to know the voltages needed.
You could try leaving a comment on the video to see if he still has the scope and can measure the voltages (video is 10 years old...).

You you could also trace the circuits near J605 to see what the voltage rails seem to be - i.e. rectifiers and regulators.
I did seem to see a 6.3V label on the transformer, so at least one of the windings would be 6.3V AC - very common in older gear.

Actually, I found a schematic here for that series of scope: https://elektrotanya.com/gw-instek_gos-620_gos-630.pdf/download.html
It shows the windings and wire colors on page 11, but doesn't call out all the voltages.  You can likely work them out (from the labelled rectified & regulated PSU outputs), but note that some are high voltages so you need to be careful.

If you don't have a suitable transformer, then this is probably scrap as it would not be worth spending much money getting it working.
Maybe your best bet is to try find a faulty one selling cheap that may have a good transformer.

3

Metrology / Re: Cost and who to adjust PM2525

« Last post by watchmaker on Today at 11:54:58 am »

I looked at the PM2521 SM.  Now I understand why the 2525 uses the motor on the selector. It looks like the same selector on both and Phillips decided the motor was the way to automate that model.  BUT, it does appear from the PM2521 SM that shorting pin 5 to pin 7 of the jack provides a trigger.  I will try this when I have time.

The other thing that is interesting is the logic levels are -10 and -5 volts.

4

Test Equipment / Re: Equipment Discounts from Saelig

« Last post by siona32030 on Today at 11:51:32 am »

Hey, I'm trying to purchase some Siglent test equipment for my new home lab.  Most likely the SDM3045X and SPD3303X, is there any code I could use for this, please?

5

Projects, Designs, and Technical Stuff / Re: Electronic load precision

« Last post by ArdWar on Today at 11:50:06 am »

I'm not sure about 5532 specifically, but input offset while can have quite wide spread tend to be quite stable over time and temperature. Once you do initial calibration (and maybe implement autozero) you can get 10s to 100s of uV performance.

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Projects, Designs, and Technical Stuff / Re: Electronic load precision

« Last post by ifonlyeverything on Today at 11:48:32 am »

Those are not the shunts that give you the accuracy.
https://www.youtube.com/watch?v=5dNxzzuMTB8&t=730s

These are the shunts, those wiggly-wire things.
The small shunts are only used for current sharing in those FETs, and the opamp is to drive the FETs, they are not used for precision measurements.

Are you sure? I assumed the 4 wire shunts (and maybe the 5W, 1R resistor) were used to measure the total current that flows through all 10 FETs. This would make sense because they have a separate specification for "readback current".

At any rate these wire shunts are likely <0.05 Ohms resistance, making the measured voltage drop even lower for a commanded current in the single milliamp range. How are they reliably and accurately sensing microvolts in the feedback loop?

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Projects, Designs, and Technical Stuff / Re: How to make a one-transistor bjt 2KHz amplifer work over 3.3 to 4.2 V Vout=1-V

« Last post by Salome2 on Today at 11:47:53 am »

PGPG.. I searched fairly thoroughly(googled) for design info on this CE biasing with neg. feedback but couldn't find anything!

I don't quite get how things will add up to functionality with adding a 100K series resistor to base and 47K C-B.

I don't think your solutions will solve the problem of temp compensation while keeping Vcol at BatV/2 over battery V range.

Does anyone know how to LTSpice this?

8

General Technical Chat / Re: FranLab is getting evicted

« Last post by nctnico on Today at 11:44:51 am »

It surprises me that the patrons are still funding this endless monetary pit.

Keep in mind lots of people are kind of sadistic and are actually enjoying other people's misery. Just look at how many TV shows evolve around perpetual personal drama and misery. 

9

Beginners / Re: Identifiying DO-7 Germanium diodes

« Last post by Andy Chee on Today at 11:42:11 am »

I'd stick them on a curve tracer, then compare then with published curves in datasheets.

10

Test Equipment / Re: Hantek dso2d15 Noise from internal power supply

« Last post by iw2evk on Today at 11:41:55 am »

Hi,

i've order a double shelded 50 ohm bnc to bnc 1mt cable.

So i suppose can take awey the DUT from scope and reduce noise.

P.s. my test are on radio device, so i suppose i due buy a 50 ohm attenuator for reduce the signal from internal scope generator to input of radio..
Or i can make the attenuator with a kit ?