Author Topic: Starting up my workbench  (Read 8333 times)

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Offline ParKel

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Starting up my workbench
« on: April 25, 2010, 06:47:50 am »
Hello everyone my name is Kelvin and I'm a new comer to this forum.

I need some advice on starting up my own workbench regarding test equipments, but before I start let me tell a bit about myself. I graduated from the University of Nevada last December with a BS Degree in Computer Engineering. I was hoping to start my career in my related field only to be met by the global economic crisis and having a trying time securing a job. So after four months of job hunting and boredom to now the present. I realized how much I missed being so busy with projects and school work. I especially miss having access to electronics lab where I used to be able to just waltz in and play around with the school oscilloscopes (Tektronix), function generators (BK Precision), multimeter(BK Precision), powersupplies(BK Precision), etc...

This brings me to my situation now. I just got my tax refund and had the briliant idea of using the money to start my very own workbench. I just ordered yesterday a RIGOL DS1052E oscilloscope (hoping to convert it to 100MHz model) since everyone who owns one seem to be very happy with it.

Now that's 1 out of 4 instruments that I want to start with. In one of Dave's video blogs he recommended the HP/Agilent 3478A bench multimeter. I've been searching around in ebay and it seems like I can get a hold of one for <$150 which is good and all. Dave seems to be very confident with it in the blog, but one thing that worries me is that the calibration dial is exposed in the front. Do I have to cross my fingers that the previous owner haven't tweaked that (I called a local calibration company and they want $137 to calibrate the specific model)? Is there anything else that enyone would recomend for a budget bench multimeter?

As for the other two instruments, I'm also looking into purchasing a function generator and a DC powersupply. So along with the multimeter my budget for these are sadly low <=$200(I'm trying to stretch out my dollars as far as possible hoping to get relatively decent equiptment).

Sorry if this seem like a ton of questions for my first post, any help is surely appreciated.

Kelvin
« Last Edit: April 25, 2010, 07:17:43 am by ParKel »
 

Offline sarain

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Re: Starting up my workbench
« Reply #1 on: April 25, 2010, 09:09:10 am »
For an inexpensive power supply I would recommend you check ebay and MPJA.
http://www.mpja.com/prodinfo.asp?number=15950+PS

I have a 0-30V 20A supply that I got off of ebay. The first one I got was DOA but the seller sent a replacement and it works wonderfully.  I have been using it for about 6 years with no problems.  MPJA sells the same one for $269 which is about what I paid for it (http://www.mpja.com/prodinfo.asp?number=15950+PS).  I know that is a little more than you had budgeted but there are plenty for much less than that too.

Edit: We use this 0-18V 3A supply in one of the labs and it seems pretty good. http://www.mpja.com/prodinfo.asp?number=14600+PS  It just depends on what you want to do with it.

I am an engineering student so I still have access to the cool toys in the EE department but I have made a point of acquiring my own equipment over the years in preparation for the day that I am on my own.  Those that are still in school might want to keep this in mind.

Also, for those that are still students (or those that still know their professors really well,) keep an eye out in your department for old equipment that is being thrown away.  When a department gets new equipment, often times the professors will be willing to let you haul off the old ones if you just ask.  This might depend on the school / department though.  Even though the old equipment may be abused or outdated it is still usually better than nothing and can serve as a stepping stone towards a better equipped workbench. 
You may even have the chance to dig into it and apply some of those troubleshooting skills.  ???

Depending on where you live, craigslist might also be worth checking out.  I got a 20A Variac for $20 from someone on there.
« Last Edit: April 25, 2010, 09:15:35 am by sarain »
 

alm

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Re: Starting up my workbench
« Reply #2 on: April 25, 2010, 09:09:56 am »
Now that's 1 out of 4 instruments that I want to start with. In one of Dave's video blogs he recommended the HP/Agilent 3478A bench multimeter. I've been searching around in ebay and it seems like I can get a hold of one for <$150 which is good and all. Dave seems to be very confident with it in the blog, but one thing that worries me is that the calibration dial is exposed in the front. Do I have to cross my fingers that the previous owner haven't tweaked that (I called a local calibration company and they want $137 to calibrate the specific model)? Is there anything else that enyone would recomend for a budget bench multimeter?
I like that one too, the only issues are a non-backlit LCD display (may be hard to read depending on your lighting), and no diode/continuity test. I think $150 is a bit on the high side, around $100 should be possible. Though if you can get some sort of guarantee, that would be worth extra. One alternative is the HP 3468A, it's almost identical, but lacks the GPIB interface (may or may not be important for you), and I think the 3478A has one extra lower ohms range. It is usually significantly cheaper. Depending on the required feature set (accuracy, resolution, auto ranging, 4-wire, current), there are various models from Fluke and Keithley that might work. For example:
- Fluke 8600A: 4.5 digit LED , auto-ranging, no 4-wire ohms
- Fluke 8800A: 5.5 digit LED, auto-ranging, 4-wire ohms, no current
- Fluke 8810A: like the 8800A, slightly newer, but AC and ohms were optional
- Keithley 175(A): 4.5 digit LCD, auto-ranging- 4-wire ohms, the -A version adds backlight, GPIB and battery were optional
- Keithley 192: 5.5 digit (6.5 digits on some ranges) LED, auto-ranging, 4-wire ohms, no current, AC volts optional, clumsy front-panel, GPIB
- Keithley 195A: 5.5 digit (but accuracy is more like 4.5 digit meters) LED, auto-ranging, 4-wire ohms, GPIB
- Keithley 197(A): 5.5 digit LCD, auto-ranging, 4-wire ohms, GPIB optional, -A version adds backlight
If you don't require auto-ranging, there are even more options.

You should be able to get any of these for less than $100 on ebay (a Keithley 197 just went for $80), some significantly less (search for completed auctions to get an idea about prices and popularity). Buying used does carry the risk that the equipment is broken, try to buy tested stuff. You'rE unlikely to get them calibrated unless you pay a lot more, which isn't worth it for relatively cheap meters in my opinion. As long as it's in the right ball park on all ranges, I wouldn't worry about it.

A broken calibration seal probably does mean that someone's tampered with the calibration, and they might or might not have known what they've been doing. I've broken the calibration seal because one of my meters consistently read .5 ohms low, even in 4-wire mode. After adjusting just the zero ohms calibration on all ranges, the resistance readings were within tolerance again.

As for the other two instruments, I'm also looking into purchasing a function generator and a DC powersupply. So along with the multimeter my budget for these are sadly low <=$200(I'm trying to stretch out my dollars as far as possible hoping to get relatively decent equiptment).
No suggestions, sorry. A low-frequency (up to a 100kHz or slightly better) function generator should be available cheap on ebay, eg. from Wavetek. Same for power supplies. Or you could get one of those cheap made-in-China power supplies, but don't trust them to be able to deliver their rated power. A power supply is relatively easy to build yourself, although that probably won't be cheaper if you have to buy all parts new. There hasn't been that much development in lab power supplies (unless you get into the programmable stuff), so I'd prefer an older one by a brand-name like HP to a new cheap one.
 

Offline Kiriakos-GR

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Re: Starting up my workbench
« Reply #3 on: April 25, 2010, 09:31:45 am »
For an inexpensive power supply I would recommend you check ebay and MPJA.
http://www.mpja.com/prodinfo.asp?number=15950+PS

 MPJA sells the same one for $269 which is about what I paid for it (http://www.mpja.com/prodinfo.asp?number=15950+PS).  I know that is a little more than you had budgeted but there are plenty for much less than that too.

Those are MASTECH products , are respected and reliable as mid range , in Greece too,
for about 20 years.  ;)
I have no experience specifically with their power supply ,  but their multimeters are more than good.   
 

Offline Polossatik

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Re: Starting up my workbench
« Reply #4 on: April 26, 2010, 09:09:06 pm »
Make your own PS. It's fun. It is the best thing I can imagine to make that can make smoke.
Real Circuit design time in minutes= (2 + Nscopes) Testim + (40 +120 Kbrewski) Nfriends

Testim = estimated time in minutes Nscopes= number of oscilloscopes present Kbrewski = linear approx of the nonlinear beer effect Nfriends = number of circuit design friends present
 

Offline wd5gnr

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Re: Starting up my workbench
« Reply #5 on: April 26, 2010, 11:35:03 pm »
Stuff to build yourself:

Super Probe:
http://mondo-technology.com/super.html (see my Youtube demo: and some stills at: http://www.hotsolder.com/2008/01/superprobe.html)


Power supply:
Elenco Model XP-720K -- Easy build (cheaper to get it as a kit). Fair design. Wish it had metering.


 

Offline ParKel

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Re: Starting up my workbench
« Reply #6 on: April 27, 2010, 02:17:53 am »
Thanks for the suggestions guys. Yeah I'm still in the process of shopping around for my lab instruments/equipment. It's a great idea suggesting that I should build my own power supply. I believe that it would make a great project. I have looked at the specifications of the Elenco power supply and it didn't seem to fit my requirement of having at minimum 0-40V @ 0-3A. So maybe I'm dreaming that such manufactured power supply exists at my price range. So I'm starting to really think of designing my own. I'm quite torn about making it switching or linear. So now its based on having to deal with filtering switching noise and having great efficiency or heat and clean power. If you guys have any concerns with either please point it out for me (as of right now im leaning towards switch based).

As for the the multimeter, the do it yourself Super Probe looks very cool. I have done something similar using a cortex microcontroller in my microprocessors class. At this point though I should probably invest in a high quality multimeter as I still rely on a cheap $20 multimeter(nothing wrong with it, but it's time to move up). I can also calibrate my DIY power supply using it. The main point is having as acurate and reliable of a multimeter I can get for my budget. As of right now I believe I'm still leaning towards HP/Agilent 3478A.

I'm still up for ideas on a function generator. Maybe I'll increase my budget on this one if I end up actually saving money for making my own PS.

Thanks again guys for all your suggestions and please keep ideas coming if you think you have better options.
 

Offline wd5gnr

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Re: Starting up my workbench
« Reply #7 on: April 27, 2010, 03:04:46 am »
No doubt you want a real DMM. The SuperProbe also generates pulses and things so it is a poor man's signal generator too. And if you build it on a breadboard it might cost $10 depending on what you have laying around. Don't forget Microchip will send you a sample CPU for free so a crystal, the LED display, two switches, and a handful of resistors.

But no, I wasn't suggesting you use it in lieu of a real DVM.
 

Offline ParKel

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Re: Starting up my workbench
« Reply #8 on: May 02, 2010, 05:41:03 am »
Hey sorry it took a while for me to respond. Just got back in town. Wd5gnr thanks for pointing that out I didn't realize that it was a function generator as well. I just scored a HP 3478A recently NIST calibrated with calibration documentation for ~$150. I thought it was a good deal as the calibration itself costs $137. Now just the function generator is left. Thanks for the help everyone.
 

Offline DJPhil

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Re: Starting up my workbench
« Reply #9 on: May 02, 2010, 09:17:32 am »
I just scored a HP 3478A recently NIST calibrated with calibration documentation for ~$150.

 :o

Good find!
 


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