Electrician Talk banner
1 - 7 of 7 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter · #1 ·
I just purchased a used Fluke 123 scope meter so I can check sine waves of DC pulses from a encoder for troubleshooting purposes.
I read the user manual, but I am still a novice at using this meter.
Should I be able to measure VAC and sine waves from a 120 VAC receptacle in my house?
I'm afraid I may have a bad meter.

thanks
 

·
Registered
Joined
·
1,768 Posts
you should be able to measure sine waves by putting the probe tip next to the insulation of a live conductor/power cord. You DO NOT need to touch the probe tips to a live conductor to get a sine wave. You should be able to put the probe tip from channel 1 (or channel "A") up to the insulation, press AUTO, and wait for a few seconds and a waveform should display.

Another safe way to check if the scope inputs are not dead is to make sure the scope channel is set to DC coupling, trigger on auto, and volt/divs around 500mv and then you just connect the negative/"ground" probe terminal to one side of a AA battery and the probe tip to the other side. You should see a "noisy" line go from one level to another, i.e.. 0 volts to 1.5 volts.

If the scopemeter is in good working order they are designed to connect to line-voltage, but if it's not in good working order I wouldn't recommend it. IIRC the 123 has channels fully insulated from each other and from everything else which would let you hook it up in ways that would make the older fluke scopemeters, and most modern benchtop oscilloscopes detonate.

If you wish to buy a scope from ebay make sure you see a waveform displayed in a picture for both channels. If you do not see a waveform assume the inputs are dead. The reliability that you expect from Fluke multimeters doesn't necessarily carry over to rebranded Phillips oscilloscopes. For those I recommend Hewlett Packard/Agilent, tektronix, or something still under warranty.
 

·
Registered
Joined
·
1,768 Posts
IIRC these scope meters have 2 scope channels and one multimeter channel. The multimeter can work while the scope channels don't and vice versa. If the scope channels work on DC then you probably have a functioning oscilloscope. Fluke oscilloscopes have a reset function, maybe try resetting it and look for a sine wave on channel a by putting the probe next to a power cord. Don't bother connecting the multimeter probes, I'm only talking about the oscilloscope probes BNCs.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #6 ·
UCONDUIT,
Sorry to keep bringing up my used 123 scope meter, but I'm not sure if my meter has bad inputs or if I do not have the meter set up right to read AC sine waves.
( Actually, I have never been trained by anyone how to use a fluke 123.)
I reset the meter according to the instructions and it reset successfully.
I set the meter to AUTO and laid the A probe on a energized cord, but didn't measure
anything on the screen.
I have A or B channel set for AC and everything else set for normal.
The TIME set to 10ms/d and volts at 500mV/d.
With my lead A or B in the end of the cord
My sine waves are all square instead of the smooth "hill" shape.
Am I simply not using this meter correctly or do you think the inputs may be fried.
 

·
Registered
Joined
·
1,768 Posts
if you put the tip of the oscilloscope probe (not to be confused with the typical multimeter probes) up to a power cord it should show something. It will not be a smooth sine wave but it should look something like one. A jagged sine wave.

I don't know what you mean by sine waves looking square, as long as they aren't "flat" then that doesn't sound too bad. At 10ms/div you should see around 6 or 7 periods: basically ac line noise. It should increase the closer the probe to a conductor. Think of the scope as a "radio receiver" and the probe tip as an "receiver antenna" and think of every 60-cycle conductor as a "transmitter antenna", the closer you are to wiring the more noise the scope will pick up.

It's a convenient way to establish whether or not the scope is completely dead. For any real measurement the goal is, of course, to minimize any 60-cycle hum.

That said, if your scope isn't picking up anything at all that is a problem. Some Fluke products carry lifetime warranties and are designed and built to last a long, long time. I do not believe that Fluke oscilloscopes are warrantied for very long, and I won't vouch for their quality.

There are other alternatives out there. The only thing really good about the 21st century fluke scopes is that the grounds of each scope terminal is isolated from each other and from the power. On a regular scope if you touch the scope ground to the hot of a 120v receptacle it would (hopefully) trip your circuit breaker because most scope grounds are actually grounded. Scopemeters are designed for making that type of connection because they were meant for measuring line voltage.
 
1 - 7 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top