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Need help understanding what to look for in finding a 1 : 1 / 1X direct probe for a Sencore SC61

24.26.2.208

Michael Norona

I need to get a 1X direct probe for the Sencore SC61 O-scope. The SC61 & SC3080 listed the DP226 & 270 as the model numbers for the Sencore 1X probes for the 61 & 3080 respectively. The description said the probes provide direct input for measuring signals in the 5 to 50 millivolt range, and frequencies up to 15Mhz. The specs for the SC61: it has a FR of + - 3db DC to 60Mhz, useable to 100Mhz. AC coupled: + - 3db, 10Hz to 60Mhz. The sensitivity is 5mV/div. to 20V/div. for direct 1X. Input impedance is 1 meg shunted by 50pF for direct 1X. Max input voltage is 500 volts (DC and Peak AC) for direct 1X.

I have read a good bit on the web about probes, and it seems as though a switchable 1X - 10X might be the way to go. There is a site I found about probes for Tektronix's scopes, but the guy said you could apply the guidelines he discusses to most probes in general. He said the most important factor was the compensation range. He said the attenuator circuit and compensation adjustment of the probe must match the imput resistance & capictance of your scope. What I can't understand is how the compensation range relates to the input resistance & capacitance. For example: one 1X 10X probe I looked at listed the input R & C as 1meg - 200pF for the 1X, and 10meg - 22pF for the 10X, the compensation range is 10-60pF. How does the 10-60pF relate to the 200pF and 22pF?

What am I missing? Is this incredibly simple, one of those kind of questions that you would see on "Are you as smart as a 5th grader. Can someone guide me through the wilderness? Thank you

Follow Ups:

RE: Need help understanding what to look for in finding a 1 : 1 / 1X direct probe for a Sencore SC61 - Michael Samra 18:24:03 01/17/12 (0)
Mike
Just get the probes we talked about on the ebay because you are measuring a 15mv signal for for your mu150.
When problems become increasingly difficult,we can always rely on our collective knowledge and seek relief.
RE: Need help understanding what to look for in finding a 1 : 1 / 1X direct probe for a Sencore SC61 - Tom Bavis 07:05:47 01/17/12 (0)
10X probes have a range of inputs that can be compensated - 1 meg / 30 pF is a typical scope input. Has nothing to do with probe tip capacitance. The voltage divider in the tip isolates the cable capacitance from the tip, so the circuit loading is minimized. 1X probes DON'T have compensation and since they don't have a divider, the cable capacitance is added to the 'scope capacitance and will load your circuit under test.

The Sencore probes have an extra voltage divider for the voltmeter input, but standard probes will work without this feature.
RE: Need help understanding what to look for in finding a 1 : 1 / 1X direct probe for a Sencore SC61 - TimFox 05:04:06 01/16/12 (0)
Compensation range: a x10 probe is normally designed to include a given oscilloscope input resistance as part of its circuit, and has an adjustable capacitor that adds to the oscilloscope input capacitance for that part of the circuit. The adjustable capacitance can compensate for a given range of oscilloscope capacitance, specified by the probe data sheet.
RE: Need help understanding what to look for in finding a 1 : 1 / 1X direct probe for a Sencore SC61 - wheezer 21:58:22 01/15/12 (0)
The SC61 is designed for 10x HV probes that Sencore supplies, good to 2K5v.
For LV, applications, the 1x will do fine but the display will be off.
Follow the voltage rating of the probes, RMS + Peak; it's real trip to heart failure if you exceed their rating.

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