HP 54501A Scope Probes ?   - Page 1
Forum section: electronics / testgear

author: ozsavran
author_rank: Newbie
timestamp: March 29, 2015, 11:32:14 am
content: Hello All,Recently got a really good deal on a 4-channel, 100Mhz HP 54501A scope, only to find out the guy excluded original probes...Screen and dial menu seems to work fine for now. We get "something" on each of the 4 channels too.When I tried the cheap chinese probes I had with my UNI-T 20MHz scope, on 25Khz square test signal of UNI-T, very jittery waveforms at different voltage levels show up on each 4 channels of HP 54501A. Even though I tried to set each of the 4 channels to the same timing and division settings. Single no-label, battered probe seller included gives a little better signal picture, but again same signal shows up on different voltage levels in different channels.The original probe for this scope is beefy HP 10432A, which says: "10:1 Probe - 10Mohm//7.5pF - For 1MOhm//10-16pF Inputs" .As I understand in my newbie research capability, this probe is actually good up to 200-300Mhz measurements. A set of 4 will cost, many hundreds of dollars more than the scope itself!!My need for 4 channels is, 3-phase AC Induction motor control in 10-50KW range. So circuits I will be probing need not be very high frequency even for control stage. On power stage, I could be measuring 400Volts regularly to 1200Volts spikes.So a set of probes that is compatible with HP 54501A, but not necessarily so high frequency capable are enough, in my case. Along with a reliable method/tool to measure the output waves without frying myself and the meager equipment I have.Or simply, I am missing something serious with scope channel settings in my laziness...Any and all comments are welcome, before my demise here! Thanks in advance for taking time to answer me.All the very Best.

author: tautech
author_rank: Super Contributor
timestamp: March 29, 2015, 07:34:21 pm
content: Welcome to the forum.Please put your country flag in your profile for local recommendations.It is likely you have not set the trigger level to be within the amplitude of the waveform.There should be an Auto setting for this.For your intended "power stage" use you would be wise to have 100:1 probes that have a much higher voltage rating than 10:1 probes, especially for those peaks you describe. There is too much energy in circuits like these not to play it safe.You must be careful to use only 1 reference point for 3 phase work, and that will be mains earth.Any new probe comes full specs of "voltage de-rating with frequency", study up on this for more understanding.For other use less than 150V the P6100 probes on ebay or Aliexpress are great and cheap.

author: Neganur
author_rank: Unknown
timestamp: March 30, 2015, 12:46:36 am
content: I don't know if I would use passive probes for this, seems like a perfect excuse to buy three high voltage differential probes (10X/100X, 25 MHz, 1400V or similar)Wasn't there some other thread in here that discussed some from ebay?

author: ozsavran
author_rank: Newbie
timestamp: March 30, 2015, 07:00:06 am
content: Dear Tautech and Neganur,Its so nice to have replies from Australia and Finland promptly, thanks for answering my call.Since both of you did not touch the input capacitance compatibility (the 7,5pF thing), should I assume that there is no need to search for that in my low frequency work, but rather focus on the voltage rating please? Should any capacitance probe work at 50Hz anyway ??The Hantek 3100 probes are 2500V rated, :http://www.ebay.co.uk/itm/Hantek-T3100-X100-2500V-100MHz-High-Voltage-Probes-/281382344975.Would you trust these?All the Best.

author: tautech
author_rank: Super Contributor
timestamp: March 30, 2015, 10:04:46 am
content: NZ not Aussie for me. Nearly 2000 Km of Tasman sea between us.Understand the input and (not plus) the probe capacitance combination determins the capacitance applied to the DUT.The probe compenstation nulls this if the probe compensation range covers the scope input capacitance.This is important for 2 reasons:Less capacitance loading of the DUT.Accurate transmission and subsequent reproduction of the waveform.(important for low energy, signal level, high frequency work)For the HV high energy circuit you wish to work on there will be negligible loading from probe insertion.Accuracy for exact waveform reproduction is also unlikely to be affected at low frequncies.Those 3100 probe are cheap, they will be fine.Note the seller has only 1 available.