ParkingLotLust
Member
Hey guys,
In lab class, we often need to feed a signal from a function generator into a circuit, then scope the signal going in, and the signal coming out (lets say Im doing a PID control lab and need to do step response).
The input signals we work with are usually in the 1Hz-10kHz range - we dont work with anything in the MHz range, at least for the moment.
The typical procedure is this: using 2 sets of really crappy alligator leads (like this), one set goes to the generator, and one set goes to the scope. The grounds and signal connections are tied together, and clipped to the input of the circuit. For all intents and purposes, this works just fine, albeit it gets a bit messy with lots of scope leads everywhere.
My proposed solution was this: I went out and got a BNC T, along with a short F-F cable. I added the T on the function generator, connected the F-F from one side to the scope, and connected to my circuit on the other side of the T. Everything worked perfect, exactly as expected, until my lab teacher walked over.
He went on about how because the scope is a 1Mohm input and the generator is a 50ohm output, by connecting them together how I have them, Im causing an impedance mismatch, Im causing signal reflections, and all these nasty things. He basically had me remove the T and my F-F cable because I was breaking things.
From my limited knowledge of the subject, it would seem to me the impedance mismatch and any reflections that may be caused would be there, regardless of using the alligator leads or the BNC cables. Is there any reason to his madness, and if so, can someone explain a little further why? Cause he sure didnt.
In lab class, we often need to feed a signal from a function generator into a circuit, then scope the signal going in, and the signal coming out (lets say Im doing a PID control lab and need to do step response).
The input signals we work with are usually in the 1Hz-10kHz range - we dont work with anything in the MHz range, at least for the moment.
The typical procedure is this: using 2 sets of really crappy alligator leads (like this), one set goes to the generator, and one set goes to the scope. The grounds and signal connections are tied together, and clipped to the input of the circuit. For all intents and purposes, this works just fine, albeit it gets a bit messy with lots of scope leads everywhere.
My proposed solution was this: I went out and got a BNC T, along with a short F-F cable. I added the T on the function generator, connected the F-F from one side to the scope, and connected to my circuit on the other side of the T. Everything worked perfect, exactly as expected, until my lab teacher walked over.
He went on about how because the scope is a 1Mohm input and the generator is a 50ohm output, by connecting them together how I have them, Im causing an impedance mismatch, Im causing signal reflections, and all these nasty things. He basically had me remove the T and my F-F cable because I was breaking things.
From my limited knowledge of the subject, it would seem to me the impedance mismatch and any reflections that may be caused would be there, regardless of using the alligator leads or the BNC cables. Is there any reason to his madness, and if so, can someone explain a little further why? Cause he sure didnt.