Do you need high-quality measurements from different sensors? If you do and you’ve spoken to National Instruments or Wiresmith Technology, then you may have been recommended compactDAQ. This article will help you understand what it is, what it is good at and what it is not good for.
compactDAQ (cDAQ) is a modular, PC based, data-acquisition hardware platform from National Instruments.
PC based means that it would connect to a standard Windows laptop or desktop. This PC will be running the software that configures, acquires and logs data from the cDAQ itself.
Modular means that you can configure a system with a mix of modules for different signal and sensor types. Some of the typical sensor types we have worked with cDAQ are:
This makes it great for a variety of measurement applications. We use it heavily in our automated measurement system projects.
A compactDAQ system consists of 2 parts:
The chassis is responsible for communicating module measurements to a computer system as well as providing timing clocks and synchronisation to all of the modules in the system.
There are two key decision points when selecting a chassis:
a) You can choose from a number of different communication systems to the PC. The most common options we see are:
b) Module Count: You can select from 1, 4 or 8 slot options for most buses although there is a 14 slot USB 3.0 chassis that launched in 2016.
The C-Series modules (which are also used for the cRIO product range) are responsible for conditioning (amplification, filtering etc.) and then encoding the signals to the digital domain. There are modules available for a variety of sensors as well as digital interfaces as well.
Because all of the conditioning is built in, that means you can normally connect sensors pretty directly to the modules making setup much easier and introducing fewer measurement errors than trying to match multiple signal conditioning stages.
Most modules have 4-16 channels and have speeds of up to 50 kS/s (although exceptions apply), and there are over 150 in the range.
The advantage to cDAQ is the modular design which means:
This makes cDAQ it ideal for experimentation or evaluation applications for physical systems where accuracy is vital, and you measure a variety of physical phenomenon such as temperature, pressures, strains etc.
There are a few limitations that do need considering when specifying a cDAQ system.
The first is that it isn’t designed to be a 24/7/365 system as it depends on USB and a Windows PC. Depending on these technologies can mean problems with Windows updates or USB sleep modes on long-term tests or measurements. When you need this level of reliability, you should consider a compactRIO which supports all the same modules but has an embedded processor designed for long-term operation. The compactRIO is harder to program though.
The second limitation we see people hit is channel count. Most conditioned modules are 4-8 channels per module which means the standard 8 slot chassis can support 32-64 channels before requiring an expansion chassis. On high channel count systems compare this to a PXI based system. The SC express range of PXI cards offers similar signal conditioning options at 16 and 32 channels per card.
The final limitation is bandwidth. For temperature, this isn’t an issue, but for more dynamic measurements such as pressure or vibration most cards are designed in the 10’s of kHz ranges. If you need faster measurements than this then again, PXI may be the way to go.
We have worked with compactDAQ primarily in lab testing and validation systems such as with Lontra to develop a test cell data acquisition system to advance the design of the Blade Compressor®. You can find more case studies on the NI website at http://www.ni.com/compactdaq/applications/
If you think this is something that might be useful you can either start configuring a system on the NI cDAQ Advisor or contact us if you want some expert help with picking out the right system and getting it running.