DAQmx Lowpass Filter Cutoff Frequency

[vanderdolino]

I am looking to enable lowpass filtering on multiple stations and DAQ boards. I had in mind that a 1MHz cutoff is a good starting point, and we already have some physical RC filters in this neighborhood. The idea is to replace any physical filters with those built into the DAQ system.

I have started with these properties found in DAQmx

Dim _channel As NationalInstruments.DAQmx.AIChannel
_channel = _task.AIChannels.CreateVoltageChannel(...)
_channel.LowpassEnable = True
_channel.LowpassCutoffFrequency = 1000000000.0

based of this page, and some more info here. However, I haven't found the latter very helpful as the task I created in MAX doesn't have a "Device" tab...

My question is, how do I know the filter frequencies available on my cards? I have not been able to find this information anywhere. Across 15 production machines, I have an assortment of DAQ cards, including 6001, 6008, 6211, and 6343, currently.

Also, do I need to select some clock source to perform the filtering? I am not sure how it is done internally in the card.

[paigec]

1. What is the frequency of the input signal(s) you are expecting vs. the cutoff frequency for filtering?

2. Have you been able to refer to the specifications for those DAQ cards? You may want to explore those for each device here.

3. Regarding the clock sourcing, what type of timing are you looking for with your acquisition?

[vanderdolino]

Thanks for the reply

1, 3. Some of the signals have slow time constants (temperatures, water flow rates, some power meters), and are sampled anywhere from 1 to 5 Hz. We also measure rise time of a signal in the 30us range. We sample that at 250kHz. This is the one we're mainly interested in filtering. We are using the cards' internal clocks.

2. I have searched the product specifications and not found anything related to low pass or cutoff. Are you aware of anywhere it is documented (6343-USB, for example)?

[paigec]

The specifications for the NI 6343 are found here, and do not list an internal cutoff frequency. As stated in this KnowledgeBase article, devices that have configurable analog input lowpass filtering should have a value for the cutoff frequency in a DAQmx Device Property Node.