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Joined: May 21st, 2018, 8:17 pm
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Post by anglenora2022 » May 21st, 2018, 8:51 pm


Please clarify the below.

When i tried to capture a signal generated from LWS data acquisition system on TDS2002B scope interfaced through a 50 Ohm bnc cable, the readings in the scope were different than that of data acquisition systems. Scope is brand new, calibrated.

settings done: in Data Acquisition system - Generate - 2khz signal @ 2Vpp for 60seconds.

Redings on TDS2002b : - 3.5KHz and 4Vpp. :roll:

1)Should there be a procedure to capture from data acquisition system? .

2)First of all i want to know is it possible to capture the data from a data acquisition systems, where you will be commanding through software to generate. ? i am correct or not?.

Pls provide technical points/ clarifications.


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Post by strick » May 23rd, 2018, 8:52 am

I really have no idea what a LWS data acquisition system is, but any function generator is expecting a target resistance on the part of the scope. Usually the scope is set to 1 Meg ohm for sampling to put a minimum load on the circuit that is being tested. Makes plenty of sense when checking values that can easily range up to hundreds of volts. Most Tek scopes also use a 10x probe that increases this initial resistance.

However, many generators expect a 50 ohm resistance at the end of the cable, not 1 Meg ohm. If you are using a 50 ohm cable, that only indicates the impedance is set to match a 50 ohm source and 50 ohm target. Thus, to get the proper 2 Vpp, you must either set the scope internal resistance to 50 ohms (using the vertical menu button) or use a bnc "T" with a 50 ohm bnc termination (the first is better). Getting 4 Vpp is precisely what you should get if it expects 50 ohm and you have the scope at 1 Megohm.

As far as the frequency being off 500 hz, you would have to specify the model of generator (I googled LWS data acquisiton and did not get anything useful..) and one might have a clue.

:) Strick

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Post by Konkol » May 25th, 2018, 5:11 am

Frequency being off by 500 hz sounds very odd to me. I've never heard of something like that. I'm really curious to hear the answers to your questions, Anglenora. I hope someone more knowledgeable pops in and sheds some light on this.

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