Modular approach simplifies acquisition setup

The Stack-DAQ range is a truly novel, low-cost range of data acquisition and control units suitable for use with any RS232 equipped PC.

The Stack-DAQ range is a truly novel, low-cost range of data acquisition and control units suitable for use with any RS232 equipped PC.

There is a wide range of analogue and digital I/O, thermocouple, pulse counter and motor control units which simply stack end-to-end on a single RS232 port: designers need only use those modules required for the task in hand.

And with the Stack-DAQ Windows software, Modcom, setting up complex data logging and control applications could not be easier.

All Stack-DAQ modules incorporate two serial ports, the host port and the slave port.

The host should be connected to a PC's serial port.

The slave port can be left open, or connected to another module's host port.

Up to 32 modules can be chained together in this fashion to form a network, either plugged together end to end, or separated by a cable.

Because each module contains two individual bidirectional ports which pass data through, it also acts as a repeater, extending the total allowable length of the RS232 communications line.

Most Stack-DAQ IO modules have built-in features not normally found in DAQ devices.

The eight-channel analogue input module has two software programmable alarm trip-points for each input channel and auto calibration.

The four-channel analogue output module has automatic generation of trapezoidal and S-curve slope profiles.

The four-channel thermocouple input module accepts J, K, T or E thermocouple types and has built-in linearisation using high-order polynomial equations eliminating look-up table interpolation errors.

The 14-channel digital I/O module responds to button presses and switch transitions, decodes 4x4 matrix keypads as well as performing standard input/output functions: there is also a solid state relay output version.

The pulse counter module can be configured to measure frequency, period, duty cycle or rotational speed from a single or multiple toothed shaft/pickup devices.

There is even a stepper motor module with built-in S-curve acceleration and deceleration slope profiles and software programmable ramp rate, velocity, and idle current.

It also has a 24bit absolute motor position counter and normally open limit switch inputs.

By far, the most painless way to communicate with the Stack-DAQ modules is to use the Windows Modcom software, a GUI-based HMI development tool designed specifically for the Stack-DAQ range.

The novice or nonprogrammer will appreciate the ease at which eye-appealing display screens can be laid out very quickly, and the ability to perform complex functions with a minimal user learning curve.

Modcom screen components include multiple screens, text boxes, data windows, status indicators with changing colours, event timers, pushbuttons, rocker switches and sliders.

Collecting data and writing it to a file is a very important aspect of any data acquisition software.

With Modcom, any screen object which is used to collect and view data can also be set up to send that data to an Excel compatible text file automatically.

This can occur at a regular user selected time interval from seconds to days, or be forced on command by any object within Modcom which is capable of executing a function.

And as the original data are being captured by a screen object, thet can be converted to the appropriate units of measurement ahead of time using the scaling and offset factors built-in to that screen object.

Conditional statements are used by Modcom to watch for certain events or conditions during run-time and then act on them by executing a function.

Such a condition may be the reception of a specific data string from a data module, an event counter which reaches a specific count value, an event timer indicating the passage of a specific amount of time, a data window which displays a reading beyond a specific set point, a level indicator which shows a value above or below a certain tank level, a signal lamp which turns on, or even a text window which displays a certain message.

Conditionals are very useful for reporting alarm trips.

One of the more powerful features of Modcom is the ability to build custom sequences for automation and control tasks.

A sequence is a list of functions that will execute sequentially during run-time when being called by other objects such as a pushbutton, a conditional, or even another sequence.

And because a sequence can call another sequence, this allows the programmer to assemble groups of commonly used tasks which can be used as subroutines of other complex sequences.

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