230V AC Wave forms in an analog ocillocope

Question

I was doing a project on AC Phase control using triac,and I needed to see the phase controlled waveforms in a scope.But the scope that I am using has maximum volts/div as 5V (found on many scopes as well), which means I can get about 25V peak to peak (there are a total of 10 division of units on screen) peak to peak voltage wave on the scope.

Is there any way to see the 230V 50Hz AC and it's phase controlled waves in a scope? If not what is the normal procedure to observe the AC(more than 25V peak) outputs of power electronics circuits in scope?

P.S. Max peak voltage at channel input of scope is written as 400V.

Answer 1

Actually, you are going to want either two probes, in differential mode, and do NOT connect the grounds, or a much better solution is to simply get a differential scope probe. Using a differential probe will keep the scope case away from line voltage, as well as make the signal in range of your inputs.

Answer 2

It is for this reason that scope probes are normally used to observe signals. For your application, 230VAC has a peak-to-peak value of 650 volts. A X10 probe will convert your 5 volts/div to 50 volts/div. But this will probably still be insufficient to display the full voltage on the screen. I would recommend a X100 probe. Be sure the probe is rated for the voltage (both RMS and peak-to-peak). Also be very careful about the grounding. The scope input is normally grounded but your AC source may not be.

Answer 3

Simple Answer - Use a Voltage Divider , and get it down to the scale range of your scope. I have tested it, and worked perfectly. Use the resistors in the scale of K's

http://www.globalspec.com/pix/EngineeringCalculators/ac_voltage_divider.jpg Something like this, just have the Probe at Vout, and the other one on GND.

Answer 4

I use a Tek TPS2024 200MHz 2GS/s 4-channel digital oscilloscope.

It has four isolated channels (from earth and from each other). Unfortunately the lawyers have got to it in my firmware revision and you have to acknowledge (or, perhaps lie) that you're not using it over 30V with the stock probes (previous versions did not have that 'feature').

When used with the optional P512x probes, it's rated for and suitable for Cat II measurements on voltages 480VAC-600VAC RMS to earth and between channels.

It's a fairly old model- requires small capacity CF cards (eg. 256M, which are scarce) to save images, which is a bit of an inconvenience.