HELP!! Why is my new sig gen reading double on the occiliscope - Page 1
Forum section: electronics / beginners

author: cpposteve
author_rank: Regular Contributor
timestamp: October 18, 2018, 10:35:19 pm
content: hi all. as the tittle suggest. why is my new UNI-T UTG1005A sig gen reading double?? the frequency is correct byt say when i set it to 1v pp it shows it as 2vpp on my scope. been through the manual and cant find it anywhere. any help would be apreciated.thankssteve

author: IconicPCB
author_rank: Super Contributor
timestamp: October 18, 2018, 10:40:40 pm
content: The instrument has a specified output voltage into specified load ( some are 50 ohm, others 75 and yet others 600ohm source/load impedance instruments).If Your signal generator is specified as having 50 ohm source impedance then You need to terminate it with a 50 load in order o see the specified signal level.The oscilloscope input impedance at lower frequencies is much higher than any of the above options hence the output voltage will be higher than specified.

author: cpposteve
author_rank: Regular Contributor
timestamp: October 18, 2018, 10:44:09 pm
content: Brill. Thanks for the answer. So how do I go about putting a signal out to a circuit? Do I have to make sure it has the 50ohm resistor/load across it no matter what I’m doing? Thanks.

author: cpposteve
author_rank: Regular Contributor
timestamp: October 18, 2018, 10:49:42 pm
content: yes you are a genius. i turned it all the way up to "HighZ" and it fixed my issue, thank you very much.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: October 18, 2018, 11:07:20 pm
content: https://youtu.be/tClE8s6RZdg

author: cpposteve
author_rank: Regular Contributor
timestamp: October 18, 2018, 11:31:40 pm
content: That’s a brill video thanks. And shows exactly what mine was doing.Another question. Without measuring what would you say is the max current draw I will be able to achieve from the sig gen? 100ma? Or does it depend on the frequency etc. New to sig gens. Many thanks

author: xrunner
author_rank: Super Contributor
timestamp: October 19, 2018, 12:53:39 am
content: Quote from: cpposteve on October 18, 2018, 10:44:09 pmNo not necessarily. If you are outputting a signal into 50 ohms then select the option that tells you what level you would see across 50 ohms. It doesn't actually change the output of the sig gen but rather tells you what you will see across the 50 ohm load as compared to connecting it to a Hi Z load.The other choice is the Hi Z option or otherwise called EMF (electromotive force). This is the total EMF the instrument would supply at the given setting for amplitude you dial up, and if you connect a very high impedance to the sig gen you will effectively see the entire EMF across the load. In circumstances involving loads not 50 ohms you are just sort of on your own and would adjust the level to achieve the desired results, such as stimulating the circuit you are interested in in the desired manner ...

author: macboy
author_rank: Super Contributor
timestamp: October 19, 2018, 02:00:50 pm
content: Quote from: cpposteve on October 18, 2018, 11:31:40 pmThe signal generator has a 50 Ohm output, which means a 50 Ohm resistor in series with the output (between the output amplifier and the jack). So when it outputs e.g. 5 V (e.g. the peak of a 10 Vpp wave), into a short circuit, the current will be 5V/50R = 100 mA. The RMS current will be around 71 mA for a sine wave. The same signal into a proper 50 Ohm load will give 5V/(50R+50R) = 50 mA peak. The terminating resistor is in series with the source resistor.In contrast to a power supply, which has a "zero" output impedance, drawing current from the 50 Ohm signal generator output will reduce the amplitude of the output.