Basic usage of a Function generator - Page 1
Forum section: electronics / beginners

author: sämäx
author_rank: Newbie
timestamp: October 09, 2016, 09:42:29 am
content: Hi I bought a function gen and now I want to check couple of things so I won't break it.1 What kind of short circuit protection does a basic function gen have a? Example what happens if I have a capacitor between my voltage rail and ground. My theory is that when I increase the frequency the reactance of the capacitor will go down and act like a short circuit. Will this break my function gen?2 How do you normally fit the impedance of the circuit to match the 50 ohms? In my understanding the impedance will change according to the frequency that’s fed in to the circuit.3 Should I keep something else important in my mid while I am experimenting with my new function gen so I won’t blow it up?

author: danadak
author_rank: Super Contributor
timestamp: October 09, 2016, 10:16:52 am
content: 1 What kind of short circuit protection does a basic function gen have a? Example what happens if I have a capacitor between my voltage rail and ground. My theory is that when I increase the frequency the reluctance of the capacitor will go down and act like a short circuit. Will this break my function gen?To answer this you have to look at generator manual. Most lab grade generators have protection.As far as C goes depends on the C. Most C's have a rising Z characteristic past a certain pointdue to internal parasitic L.2 How do you normally fit the impedance of the circuit to match the 50 ohms? In my understanding the impedance will change according to the frequency that’s fed in to the circuit.The generator sources 50 ohms via circuit design, same is true for load.There are many methods to Z match load to source,http://electronicdesign.com/communications/back-basics-impedance-matching-part-1If you are working with LF types of applications, audio for example, Z matching not consideredan issue if load is high Z. That will impact generator Vout.3 Should I keep something else important in my mid while I am experimenting with my new function gen so I won’t blow it up?Have on hand attenuator pads and start with a 20 db pad when applying fgen to circuit,that will protect you in almost all applications where voltages and power levels are smallsignal based. fgens and scopes on 50 ohms get toasted often because power is exceeded.If you have a load that can source power use a pad. Note the manual usually discussesoperator safety for the fgen, methods and approaches.http://cp.literature.agilent.com/litweb/pdf/5989-8790EN.pdfRegards, Dana.

author: rstofer
author_rank: Super Contributor
timestamp: October 09, 2016, 04:29:07 pm
content: Interesting and timely subject. I'm just about to buy a Rigol DS4160 waveform generator. So, I read the manual...Quote

author: rstofer
author_rank: Super Contributor
timestamp: October 09, 2016, 07:52:06 pm
content: If your load is high impedance, you can put a 50 ohm resistor across the FG leads, right at the input. You can also put a coax 50 ohm thru-terminator right at the end of the coax before the pigtails (whatever) hooks into the circuit.If your load is low impedance, you can put a 50 ohm resistor in series with the FG leads.The FG metering may depend on the output being terminated at 50 ohms or you may be able to select between assuming Hi-Z and 50 ohms for metering.No link to the FG was provided so no totally correct answer can be given. But the guidelines from others (above) will provide for a safe operating condition.