P5205  high voltage differential probe - tektronix - Page 1
Forum section: electronics / testgear

author: jorbefer
author_rank: Newbie
timestamp: September 11, 2018, 02:19:38 pm
content: Hi, I have recently bought an oscilloscope from ebay. This probe came included in the purchase and I am pretty new with electronics and differential probes.I want to know if even if this is a differential probe, is it isolated? I want to use it mainly for old radios, power supplies etc and I don't now if i still need to isolate the oscilloscope and/or the equipment that is under test to avoid shorts/damage.Thanks for your time.

author: bitseeker
author_rank: Super Contributor
timestamp: September 12, 2018, 02:05:10 am
content: Those probes are exactly what you want so that you don't have to worry about damaging your scope due to improper ground placement or exceeding the maximum voltage of the scope's input. Just make sure that you have the probe at the correct setting (50X or 500X) for the maximum voltage you'll be measuring/viewing (the probe does have limits). Set it too low and you'll damage the probe. Use it properly and you can probe with it like you would with a DMM. Very convenient.

author: mtdoc
author_rank: Super Contributor
timestamp: September 12, 2018, 04:21:14 am
content: I have one. They’re excellent differential probes. Manual can be foundhere.They do require a Tekprobe interface to be powered. Does the scope have that ? If not you’ll need a Tektronix 1103 Tekprobe power supply.Great score to get one of those with your scope BTW.

author: bitseeker
author_rank: Super Contributor
timestamp: September 12, 2018, 05:26:54 am
content: Yeah, they're pretty pricey probes.

author: Jim Narem
author_rank: Contributor
timestamp: September 12, 2018, 05:40:12 am
content: The manual implies that you can't damage the probe by selecting the wrong attenuation setting. In the "nominal specifications" there is a table for the maximum nondestructive differential input voltage. For the P5205 it's +/- 2KV DC. My P5210 just beeps when the setting is wrong and it gets overloaded. Note that there is a frequency derating curve too.

author: bitseeker
author_rank: Super Contributor
timestamp: September 12, 2018, 05:55:13 am
content: Ah, very good. That makes sense for this class of equipment, now that you mention it.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: September 12, 2018, 10:05:38 am
content: To answer your question about isolation. The probe is not really isolated, both leads are referenced to the scope ground and there is a separate rating for the maximum voltage of the leads to ground and between the two leads.The reading on the scope will be the differential voltage and for most practical purposes you can treat this as an isolated probe, since both leads have very high impedance to ground.

author: bitseeker
author_rank: Super Contributor
timestamp: September 12, 2018, 05:02:28 pm
content: Yes, and for this reason (as well as safety reasons), do not float your scope. The probe needs the ground reference from the scope.

author: duak
author_rank: Super Contributor
timestamp: September 12, 2018, 10:57:14 pm
content: I've got one of these things. It's a handy gizmo great for checking out off the line power supplies. One thing to be aware of is that each input of the probe presents a DC resistance to 'scope ground of a few megohms in parallel with a few pF. If the circuit under test is not referenced to 'scope ground or is at line potential, the probe can draw from or inject a current into the circuit. If the circuit node is high impedance or sensitive to sub milliamp currents, the circuit operation could be affected. Bottom line, be careful probing the lower level parts of circuits.I connect the probe '-' input to the circuit's common first to get a feel for any common mode voltage and then use the '+' input to look at voltages relative to that.I've attached a snapshot of the input circuit.