Simple PC-based data acquisition cards are adequate for a less complex measurement and control systems. However, the more complex measurement and control systems, typically those with more than 32 channels of input and output can present different challenges and will require a more robust solution.
DAP boards from Microstar Laboratories, with their unique Channel Architecture, can solve many of the problems associated with complex test and measurement systems.
Connecting all the signals
Connect many wires from the sensors to the measurement system. The edge of a PC expansion card is suitable for wiring small measurement and control systems, but for the complex systems both the initial wiring and the inevitable wiring maintenance could prove to be problematic.
All those wires: easier to set up, easier to maintain.
19-inch rack-mount Industrial Enclosures provide up to 20 slots for expansion cards. They also provide front panels for connectors including BNC connectors, which cannot easily fit on standard computer cards.
dealing with ground loops
Complex systems can give rise to ground loop problems. These may occur when several sensors are connected to the same ground in a measurement system. Resistance in ground paths can cause a ground current in one sensor to interfere with the measurements from another sensor. The more sensors in a system will usually mean a large physical size so grounds are further apart, giving these problems.
Eliminate ground loops with channel-to-channel or channel-to-PC isolation for digital and analog signals. Input and output isolation modules are available for voltages and 4-20mA loops.
Processing slow and fast channels at the same time
Sampling times in complex systems may vary widely. For example, it may be appropriate to sample a strain gauge a few thousand times per second, but a temperature sensor could be sampled once per second. With just a few sensors it makes sense to sample at the highest rate required by any of the sensors. This can easily exceed the bandwidth available for a PC or its disk storage system, therefore a better solution is required.
The DAPL real-time operating system on a DAP board provides on-board software tools for separating slow and fast channels. These can be passed to the PC through multiple “pipes”, simplifying the PC software for logging and visualization.
Managing all the data
Organizing the data from so many sensors can easily overwhelm a PC. With a basic data acquisition system, the PC reads all the data from all the channels, some of which is not needed. The PC then tries to reduce the data volume while logging to disk and plotting the graph.
A real-time operating system and dedicated software can reduce the flow of data, without any overhead in the PC. The DAPL real-time operating system on a DAP board provides many onboard software tools for data reduction, including:
- Averaging
- Filtering and decimation
- Software triggering
DAPL real-time operating system
A PC that is managing a large number of channels can have an unpredictable latency, which makes it unreliable for control applications. This is because it typically runs many concurrent tasks such as mouse update, system maintenance and drawing graphs. To operate quickly many tasks are performed in blocks e.g. store data, but this means the computer cannot react to the latest data immediately.
For further details on DAP systems for real-time or large data acquisition systems please click here. Alternatively please contact our Measurement & Control application engineers on 01273 570220 or email sales@amplicon.com.
