Reference signal lock in amplifier

[MichaGue_01]

Hello,

i just found the lock in startup kit which I foun very interesting.

http://digital.ni.com/express.nsf/bycode/lockin?opendocument&lang=en&node=seminar_US

I am using a 6115 to aquire sinus waveforms. Sometimes the waveforms are very low, so the noise could be a problem. The lock in method would help a lot.

Question

Must the reference signal be also a sine wave, or could I use the sync signal (square waveform) out of my function generator (Agilent 33220A) which the sine wave performs?

The sync signal has the same phase and frequency as the sine wave but a constant amplitude of ±5V. The problem is that the sine wave varies from ±20mv to ±5V and if it is very low the quality of the aquired reference is not as good as it should?

Thanks a lot and best regards,

Michael

[thomas.weskamp]

Hi Michael,

this is Thomas from NI Germany, and I will try to assist you in your issue. 

For the current version of the LockInPLL.vi to function properly, the reference signal must be symmetric around 0. The Param control parameter may be used to offset the reference

signal if that is not the case. For example, if a TTL signal is to be used as a reference signal and its levels are between 0.5 and 4.8 V, then the value of the parameter

should be about   (4.8 – 0.5) / 2 ~ 2.2 V  The Default value: 0 You can use the square signal, but if it is not symmetric around zero, you need to set the Param control to this value.

In case of your +- 5V value, this should fit exactly.

As for your 20mV signal, you first should ensure that you are using applicable cables to avoid noises, and that the source of the signal itself does not create the noise.

Let me know if this was helpful for you.

Regards

Thomas

[thomas.weskamp]

Hi Michael,

since I did not get a response from you for a couple of days, I do believe that there is no further question from you.

So this issue will be closed automatically within 5 days.

Regards

Thomas

[MichaGue_01]

Hi Thomas,

thanks a lot for ypur answer. Just another short question for the lock in amplifier.

- I know the frequency of my acquired waveform

- I know, that the original one is a sinus

- I know the sampling rate

- And I know how many cycles I have aquired

Does it work that I generated the reference signal with this information. I mean, I can generate one via software?

Thanks a lot for your help.

Best regards,

Michael

[smercurio_fc]

---

@thomas.weskamp@ni.com wrote:

Hi Michael,

since I did not get a response from you for a couple of days, I do believe that there is no further question from you.

So this issue will be closed automatically within 5 days.

Regards

Thomas

---

You can't automatically close an issue that's posted on this forum. Only the poster of the question can mark a response as a solution and even then the thread can still be continued.

[thomas.weskamp]

@smercurio_fc: Yes, you are right, I mixed up some things. Sorry!

@Michael:

I am sure that there will be any way to generate a trigger, but I think that you are running a windows system, true?

Are you sure that the jitter from your software generated trigger to the action you want to trigger is that exact as you need it?

Regards

Thomas