Author Topic: Question about voltage on rigol  (Read 9331 times)

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Offline guitar309

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Question about voltage on rigol
« on: December 17, 2010, 03:08:19 am »
I am a long time eev blog stalker lol... I have been thinking about buying a Rigol scope now for some time... My only concern is I think the ds1052e is rated for 400 volts...  I am new to the oscilloscope world and knowing that there are some high voltages (over 400) in a guitar amp I am concerned that this scope will not work for what I need it to do... I am mostly wanting to use the scope for biasing tubes and such... but don't want to burn it up... any suggestions??
 

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Re: Question about voltage on rigol
« Reply #1 on: December 17, 2010, 04:10:26 am »
high volt x1000 probe. check out dave's video with doug ford... http://www.eevblog.com/2010/05/08/eevblog-85-high-voltage-oscilloscope-probe-design/
« Last Edit: December 17, 2010, 04:12:42 am by shafri »
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Online NiHaoMike

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Re: Question about voltage on rigol
« Reply #2 on: December 17, 2010, 04:48:44 am »
You'll need an isolated probe if you're working on high voltage mains power supplies. I'm actually looking at how to build one. (I'm thinking of modulating a RF carrier at least 10x the maximum signal frequency, isolating that with an RF transformer, and performing synchronous detection.)
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Online Simon

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Re: Question about voltage on rigol
« Reply #3 on: December 17, 2010, 04:47:20 pm »
any scope will have an input of not more than 30-50V you will adapt this with probes, 10X probes are very common and supplied by default. 100X probes and 1000X times probes will cost more than the scope !, what voltages are you measuring ?
 

alm

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Re: Question about voltage on rigol
« Reply #4 on: December 17, 2010, 10:01:04 pm »
any scope will have an input of not more than 30-50V you will adapt this with probes, 10X probes are very common and supplied by default.
Not all 10x probes will be rated for 500V, however. Most are lower. The max. input voltage is also derated with frequency.
 

Online Simon

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Re: Question about voltage on rigol
« Reply #5 on: December 17, 2010, 10:05:22 pm »
ah yes true, so there you go OP, even more complications
 

Offline Neilm

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Re: Question about voltage on rigol
« Reply #6 on: December 18, 2010, 10:36:44 am »
If measuring high voltages, remember that the capacitance of the scope probe can have an effect on the displayed signal.

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Re: Question about voltage on rigol
« Reply #7 on: December 18, 2010, 12:18:16 pm »
it would be interesting to know the expected voltage, I measured 400 V back EMF spikes with no problems
 

Offline guitar309

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Re: Question about voltage on rigol
« Reply #8 on: December 18, 2010, 05:54:57 pm »
The amp I am currently using has a plate voltage of just over 500v... From what I am hearing it might be safe to go ahead and get a different probe so I don't damage anything... There is a company called weber that makes some amp repair tools.. They make a great dummy load for amps that is selectable for 4,8,16 ohms and also has connection leads for a multimeter and a bnc connector for an oscilloscope so does anyone know where I could find a probe that is (I guess) bnc to bnc ?
 

alm

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Re: Question about voltage on rigol
« Reply #9 on: December 18, 2010, 06:21:46 pm »
Many probes come with a probe tip to BNC adapter, allowing you to plug the probe into a BNC socket. Regular BNC-to-BNC coax cables are very different from probes, and are designed for low impedance (eg. 50 ohm) environments.
 

Online NiHaoMike

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Re: Question about voltage on rigol
« Reply #10 on: December 19, 2010, 02:30:32 am »
The amp I am currently using has a plate voltage of just over 500v... From what I am hearing it might be safe to go ahead and get a different probe so I don't damage anything... There is a company called weber that makes some amp repair tools.. They make a great dummy load for amps that is selectable for 4,8,16 ohms and also has connection leads for a multimeter and a bnc connector for an oscilloscope so does anyone know where I could find a probe that is (I guess) bnc to bnc ?
It's very easy to make a BNC cable. Just take a piece of coax (50 ohm is more standard in test and measurement, but 75 ohm is more common in consumer electronics) and put a BNC connector on each end. And unless your oscilloscope has built in termination, you'll also need an inline terminator that matches the cable. Otherwise, you'll get severe distortion in your signal. (Use the BNC cable to connect the oscilloscope to a pulse generator (or function generator set to square) without termination and you'll know what I mean. Then install the terminator at the oscilloscope and watch the waveform improve.)

As for working on high voltage mains circuits, you'll either need an isolation transformer large enough for the equipment you're working on along with a high voltage probe or an isolated high voltage probe. Or use a battery operated oscilloscope that is double insulated, or if you have one, use a high voltage bench power supply to power the circuit you're working on. The "ground" rail in most primary mains circuits is connected to the hot side by the rectifier circuit so connecting that to power ground will cause a short circuit.
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Offline guitar309

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Re: Question about voltage on rigol
« Reply #11 on: December 19, 2010, 03:11:24 am »
sorry I am kind of new to the oscilloscope world... just trying to put together a set up to bias guitar amps... I am also looking at the instek 1062a ... looks like a nice scope also but again only 300 volts... So.. what exactly do I need... I have been trying to read up on what I am looking for.. I see High voltage probes online.. but are all probes interchangeable? It seems instek does not make a High voltage probe for the 1062??


Sorry for so many questions... I am just lost on what I need... 
 

Offline guitar309

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Re: Question about voltage on rigol
« Reply #12 on: December 19, 2010, 03:29:32 am »
ok... after reading some items... I think if I am taking the reading off the dummy load ofter the output transformer... So I am betting the voltage is not as much as the plate voltage... ??

here is some info I have found..

http://www.duncanamps.com/technical/scopebias.html

also here is the dummy load with bnc I was talking about... so I think I will be ok with just a standard scope??   

https://amptechtools.powweb.com/truload.htm


So what do you think... Rigol or Instek?
 

alm

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Re: Question about voltage on rigol
« Reply #13 on: December 19, 2010, 12:19:00 pm »
It's very easy to make a BNC cable. Just take a piece of coax (50 ohm is more standard in test and measurement, but 75 ohm is more common in consumer electronics) and put a BNC connector on each end. And unless your oscilloscope has built in termination, you'll also need an inline terminator that matches the cable. Otherwise, you'll get severe distortion in your signal. (Use the BNC cable to connect the oscilloscope to a pulse generator (or function generator set to square) without termination and you'll know what I mean. Then install the terminator at the oscilloscope and watch the waveform improve.)
You also need a source (like that pulse generator) with matching output impedance. Unless it's a buffered output, I wouldn't expect to see 50ohm in audio. You would also have to observe power limits of your termination, anything close to 500V will burn it, plus the scope's input may not survive. But the output voltage is probably much lower, unless you're dealing with electrostatic speakers. A 50ohm, 0.5W terminator is only rated to 5Vrms, however, so even a standard amplifier output could fry it.

A probe would be preferable in that case, since it minimizes loading (both resistive and capacitive). The dummy load appears to be designed for Hi-Z (eg. 1/10Mohm) scope probes, like a standard 10x probe. The BNC socket is just there because most probe tips can be adapted to BNC. Probe tip sockets are not standardized and much more expensive and rare.

Instek vs. Rigol, from what I've read on the forum, the Instek appears to be the superior product.

Few scopes will allow you to directly connect to >300V, but there's really no reason why you'd do that without an attenuating probe. 1x probes are only useful because they allow you to see small signals, and won't be rated for >300V anyway. 10x probes attenuate the signal by 10x, so the scope will only see 10% of the amplitude (50V for a 500V signal). The only catch is that probes are also rated for a limited voltage.

In the tube world, 100x probes appear to be popular. They attenuate the signal by 100x, and are usually rated up to 1000V or so. Probes are interchangeable, as long as the scope's input capacitance is within the probes compensation range. See Choosing A Probe. 100x probes are much rarer than 10x probes, however, so they'll be harder to find and more expensive. Good probes are expensive, don't expect to get a good probe for $10, they're not just cables. Brand name 100x probes are probably close to the price of an Instek/Rigol DSO, no-name brands or used will be cheaper.

If you don't need to measure the high voltages directly, you may get away with a 10x probe, but keep in mind that you can fry something (or even get hurt) if you touch the probe to the plate voltage.
 

Offline Psi

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Re: Question about voltage on rigol
« Reply #14 on: December 19, 2010, 01:11:54 pm »
dunno how good it is but DX have a 100x probe for $32

http://www.dealextreme.com/details.dx/sku.35610
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Re: Question about voltage on rigol
« Reply #15 on: December 19, 2010, 05:14:34 pm »
You'll need some form of isolation for working on primary mains circuits and at least a CAT II rating if it's directly connected to mains.
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Offline Wim_L

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Re: Question about voltage on rigol
« Reply #16 on: December 21, 2010, 04:52:24 pm »
There are a few different options.

Applying high voltages to the scope directly is not recommended. Sure, most scopes are perfectly capable of handling a few hundred volts, on recent ones it's usually printed next to the inputs together with a CAT number. Usually the number will be CAT I, only for use on devices isolated from the mains, but CAT II and up are sometimes also seen. In principle, this means you can connect it to mains power, as long as you keep in mind that the outer BNC conductor is connected directly to ground on most scopes, and all outer conductors are thus also connected together (there are exceptions, but it's true for the vast majority of scopes). Making a connection between the outer shield and a live wire will at the very least trip a circuit breaker somewhere. If you're unlucky, it will also destroy part of the equipment.

Some scopes have 50 ohm, or switchable 1 Mohm / 50 ohm inputs. The 50 ohm ones can usually only handle a few volts at most (average over time) before the internal resistor overheats.




The next step up are passive probes, the usual stuff that comes with many oscilloscopes as a standard accessory. Often 10x, sometimes switchable 1x/10x. They're also available in 100x, 1000x, but those aren't usually delivered with the scope. They're also single-ended, the reference wire connects to the outer conductor (ground) so all the same warnings as for connecting something directly to the scope apply.

What can be done if you need a differential measurement is measuring the difference between two channels, each with the ground lead clipped to ground. Some folks simply clip the ground leads of both probes together, leaving you with two crocodile clips dangling together between your probes, just begging to short something out by accident. If a ground point is available at the device being tested, you might prefer to use that instead. If one isn't available, perhaps see if you can get good results without ground leads at all (will pick up noise). Taking the difference between two channels obviously requires that both channels have the same voltage setting. Accurate measurements also require both probes to be perfectly matched, and both oscilloscope channels to have identical performance and good common mode rejection (CMRR). They probably don't, so this is only useful for measurements that do not require high accuracy or with little common mode signal.

1x passive probes are useless if you want to measure voltages higher than what the scope can handle on its own, as they are just direct connections without attenuation.

10x passive probes may offer a somewhat higher voltage range than the scope itself, but usually not by much. It's rare to see one rated for more than 600V. 100x probes often do allow significantly higher voltages, I've got one that is specified for up to 2.5 kV for example. These are quite similar in physical appearance to 10x probes, though you might notice somewhat more insulation enclosing the terminals than on a 10x probe. Price is reasonable too, perhaps two or three times what you'd pay for a good 10x. Perhaps worth having even if you don't habitually measure high voltages because these also offer a higher impedance at the probe tip, and usually have fairly decent bandwidth too. 1000x probes tend to be bulky and expensive monsters with poor bandwidth. For 10kV and higher voltages usually. Only get these if you really need them.

Probes may also have a CAT rating on them, just like the scope. If you have a passive CAT III probe, and the scope is CAT I, stick to the lower rating, as it's really a direct connection.

Also, be very careful when using a passive probe at voltages higher than those the scope itself is rated for. For example, suppose you are using a 100x 2.5kV passive probe to measure 2kV on a scope rated for 400V. That's fine as long as you keep the oscilloscope DC coupled. If you accidentally switch to AC coupling, you can destroy the AC coupling capacitor in the oscilloscope, and perhaps a bit more of the input circuitry too depending on what happens to be near that cap.




Then, the better option (well, certainly safer). Active probes, which have active components built in and need a power supply or batteries. There are some single-ended and differential ones for high speed low voltage work. Not useful here. The ones you want are differential high voltage probes. These are high voltage amplifiers that take the difference between two inputs, attenuate it, and convert it to a single-ended output, usually a BNC cable that connects directly to the oscilloscope, or through a 50 ohm terminator (depends on the probe). The inputs and the output are (mostly) isolated from each other (some very high impedance connection may exist, but it will be almost negligible). That also means that the CAT rating of the probe applies when making measurements.

Lots of variations available with different maximum bandwidths, measurable and maximum differential and common mode voltages, attenuation factors, input impedance, CMRR... Better specifications will cost you more, and they're not exactly cheap to begin with. Be sure to check their specifications thoroughly before buying to see if they meet your needs.




Oh, and also consider derating, for both active and passive probes. The maximum permissible voltage is for DC and low frequency measurements. Most probes will not meet that specification at high frequencies, and if your probe comes with a manual it will probably contain a table or graph showing how high the maximum allowable voltage is at various frequencies. For differential probes, there will also be a derating curve for CMRR.
 

Offline nixxon

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Cheap 40KV probe
« Reply #17 on: October 09, 2012, 12:08:37 pm »
dunno how good it is but DX have a 100x probe for $32

http://www.dealextreme.com/details.dx/sku.35610

Any chance the following US $89.99 "high voltage" probe may be used to probe the high voltage CRT section of i.e. a Tektronix 422 (with CRT "Accelerating potential: Approx. 6 KV (gun potential, - 1400 volts)?:

http://www.aliexpress.com/item/Brand-New-High-Voltage-probe-for-digital-multiMeter-max-40KV-DC-28KV-AC-1000Mohm-input-impedance/545750502.html

SPECIFICATIONS ( 20 +/- 5deg. C, RH < 80% )
! WARNING !
Before taking any measurements, first connect the alligator clip of this probe to earth ground and make sure connection is electrically good.
Input impedance:1000MOhm
Division Ratio:1000 : 1
MAX. Test Voltage
DC : 0 - 40KV
AC : 1 - 28KV ( 50 / 60 Hz )
Safety APPL.
EN61010 UL3111-1 TUV / GS
IEC 1010 CAT II Pollution 2
Polarity:Positive / Negative
Accuracy
DC : +/- 1% to 20KV
+/- 2 % to 40KV
AC : - 5 % to - 10 % ( 1 - 28KV ; 50 / 60Hz )
Temperature Cofficient:</= 200ppm / deg. C
Maximum loading Current:</=  40uA ( at 40KV DC )
Maximum loading power:</=  1.6 watt
Operating temperature:0 deg. C ~ + 50 deg. C
Storage temperature:- 20 deg. C ~ + 70 deg. C
Ground Lead length:90cm ( 3ft )
Output cable length:100cm ( 3.3ft )
For:DMM
Output Division:1V / 1KV

Weight:about 300g
Remark:For 10MOhm input impedance
DMM ( Accuracy < 0.5 % ) only.



Hey, it is "Made in Taiwan by Tektronix OEM manufacturer"!! And it even has a CATII return policy :D

I was planning to do the measurements with a Fluke 83V (10 MOhm < 100 pF).


 

Offline G7PSK

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Re: Question about voltage on rigol
« Reply #18 on: October 09, 2012, 05:31:29 pm »
You could build your own attenuator, like one of these shown here.
 

Offline nixxon

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Re: Question about voltage on rigol
« Reply #19 on: October 09, 2012, 07:38:02 pm »
You could build your own attenuator, like one of these shown here.

Thanks for you suggestion.

I notice that there are BNC-connectors going in and out of your suggested circuit. Is it designed to be used with an oscilloscope with 1 MOhm input impedance, rather than a 10 MOhm DMM?

And - isn't there a risk that 6KV may spark 6 mm or more, depending on electrode shape, humidity, air pressure, temperature etc? That probably implies that some precautions should be taken before attempting to make a DIY high voltage probe.
 

Offline T4P

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Re: Question about voltage on rigol
« Reply #20 on: October 10, 2012, 09:12:39 am »
Doug shown his HV probe before ... with his mate Dave!
 


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