Re: sampling rate

From: Signal Recovery
email: info@signalrecovery.com
Model: 7225
Date: 03/02/03

Comments

You will have to use the curve buffer to get these data acquisition rates. LabVIEW has too much of an overhead to allow the PC to send a command to the instrument and record a response at anything over a few tens of hertz. In any case the instrument limit is 200 responses/second.

The basic curve buffer in the 7225 can store data to the instrument's memory at a maximum rate of 200Hz (5ms per point). At this rate any combination of outputs can be stored. The rate and the outputs to be stored are set in the Configure Curve Buffer VI.

There is a special rate that applies when you set the time per point to 0ms. This actually runs the buffer at an 800HZ sampling rate (1.25ms per point) but ONLY X AND Y outputs are stored. Setting this rate also automatically forces the X and Y outputs to be selected for storage.

Taking data any faster than this is only meaningful if the time-constants you are using are in the FAST range, i.e. below 5ms. In this case you can take X and Y or X and Magnitude readings by coupling the FAST X and FAST Y/MAG outputs on the rear of the lock-in to the ADC1 and ADC2 inputs. You then need to use the transient recorder mode, which will allow you to record X and Y/Mag at rates of up to 17.8kHz (minimum of 56us per point) It may sound illogical to use an analog connection at this point but it is necessary because in this mode the front-end of the lock in is running entirely independently of the microprocessor and aux ADC section. You will also need to arrange a hardware trigger to indicate the point in time at which the data recording should start.