Datalogging in an optics lab

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Joined: Wed Feb 14, 2018 8:07 pm

Datalogging in an optics lab

Post by DWilken »


I'm working in an optics lab and we plan to set up a system to continuously log and monitor environmental data. This especially means that we want to measure the voltage output of up to 20 photodetectors. In general, these detectors have an output range of -5V to 0V. The minimum requirement is to get data every second per photodetector. Faster sampling rates would be nice. A resolution of 12-bit should be sufficient. We want to combine the photodetector data with data from additional sensors from within the lab or from outside.

Our idea is to work with Labview. However, the PicoLog Software looks promising as well. I'm not sure if the PicoLog 1000 Series or ADC-24 is the better choice. Therefore, some questions:

-What are the sampling rates for the different data loggers independence of the channels used? The 1000er Series can do >1kS/s in Continuous streaming mode. What can the ADC-20/24 do? Is there something like a "fast mode" reducing the resolution?
-If I save the data in the continuous streaming mode what is the needed storage space on the pc per channel at the maximum rate, roughly?
-The 1000er Series does not provide a galvanic isolation. Are there any (third party) products available that isolate USB connections?
-There are LabView drivers/examples available for both devices to access the data logger directly. Is it also possible to access the PicoLog database externally, e.g. using LabView? Is it possible to write external data into this database?
-I haven't looked into you scopes yet. Is there a low price scope that has a higher input voltage range so that we can avoid additional electronics to convert the signals?

Sorry for this long list of question. Looking forward to your help!



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Joined: Mon Aug 11, 2014 11:14 am

Re: Datalogging in an optics lab

Post by Gerry »

Hi Dennis,

To answer your questions, there is no sample rate for any of our data loggers that is independent of the number of channels used. Our data loggers only have one converter (ADC) that is shared among channels, which means that every doubling of channels used, halves the sample rate. So, for instance, if you were to use 20 input channels on two 12-bit PicoLog 1216 data loggers, the maximum 1kHz sample rate for PicoLog streaming mode is reduced to 31.25 Hz on one channel. This would be the fastest that you could capture data using PicoLog, but with our Software Development Kit you could stream the data at 100kS/s for all shared channels, which means that for 2 loggers sharing 10 channels each you could achieve a 10kS/s sample rate.

The fastest you can access/convert the data in an ADC 20/24 will be almost 17 Hz per channel (the noise free resolutions are specified on page 11 of the ADC-20/24 Programming and User Guide, for the input range you want to use, here: ... -guide.pdf)

Using the 12-bit PicoLog 1216, for a 10kS/s sample rate per channel, you would need to be able to store 20K bytes every second (2 bytes of data every sample)

There are third party products that provide galvanic isolation (i.e. isolating both the signal and supply lines of USB) but be aware that the isolated ground would still be shared among channels. You can find a number of vendors that provide USB 2.0 isolation, however, you may need to test the isolator to see if it can correctly handle our USB startup/enumeration etc (as not all isolators can) and you will need to decide to what voltage you need the isolation.

By PicoLog database, I assume that you mean storage. The data isn't stored in a database. The data for the PicoLog 1000 series is first captured and held in an 8kS hardware buffer, and then transferred to the memory buffer used by the Driver for the PicoLog 1000 series. If you have opened the device synchronously, then once the capture has been completed you can transfer the data to your application memory, or you can open the data asynchronously to access raw sample data as it is being captured. The hardware and driver storage for our devices is always read only, however, you can hold data in your application storage space which can obviously be modified by you.

You can look at using one of our 2000 series PicoScopes (which have input ranges up to +/-20V) here:
However our Scopes have considerably fewer inputs, so, for instance, if you wanted to use our lowest cost 2204A PicoScopes (which would also work with PicoLog) you would need 10 of them for your 20 input application, and that is the limit of the number of Scopes that you can have on one PC.


Technical Specialist

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