Data acquisition can be simple

By Dan Hebert, PE, Senior Technical Editor

NEW REQUIREMENTS and regulations are being foisted on your customers all the time, and many of these rules necessitate acquisition and recording of data. This information might be needed to satisfy regulatory edicts, comply with internal audit procedures, or meet customer demands.

Unfortunately, existing control systems often can’t accept new inputs easily, or store data from same. Problems with adding inputs can include simple tasks such as running new wires from a remote monitoring point, and more involved jobs such as revalidating part of a complex control system just to add one data-monitoring point.

You’ll want to be sure your customers are up to speed with compact data loggers. These devices offer a solution to this problem. Although these products have been around for years, recent technical advances combined with open standards have cut costs and eased implementation. 

Compact data loggers are available to fit most any data-acquisition application. Some units combine the multiple functions of sensing, converting sensed signals to digital form, and storing digital data. Other units just store digital data, typically prodigious amounts for their relatively small size. Still other units can be installed on a PDA and directly connected to sensors.

Many of these compact data loggers are battery-powered, so no new wiring is required from a power source to the measurement point. NEMA and IP ratings vary and can accommodate environments ranging from benign to hazardous.

A typical multi-function compact data logger is made by Onset Computer Corp.. Its battery-powered Hobo data loggers range in size from 2.8x1.3x2.3 in. to 6x3.7x2 in., and some models weigh less than an ounce. These data loggers contain a sensor, an A/D converter, and non-volatile data storage. Prices start at $55 and range upward as features are added. Different models are available to measure 18 parameters, including temperature, humidity, voltage, current, wattage, pressure, carbon dioxide, light intensity, vibration, water level, and wind velocity.

Onset’s data loggers connect to a PC for initial configuration, and reconnect later for downloading stored data to the PC. “Our data loggers can be deployed in almost any situation or environment, and, if needed,  can collect data unattended for up to a year to,” says Frank Deshaies, Onset’s product marketing manager.

Acumen Instruments makes Compact Flash-based data loggers. These units are designed to accept an RS-232 serial data input, and they use removable flash storage. “Our data logger captures ASCII or binary serial data and is smaller, more rugged, uses less power, produces less heat, and requires less boot time than a PC. Many of our customers come to us because they understand the high total cost of ownership for custom-programmed PC-based loggers,” says Joel Hagen, Acumen’s vice president.

A third type of compact data logger is designed to work with a handheld portable PDA. One example is Datastick Systems’ vibration spectrum analyzer. This PDA-based vibration analyzer has a module that attaches to certain brands of PDAs running the Palm OS. The module is connected to standard ICP-type industrial accelerometers. The module includes software that collects and stores vibration measurements. The module also displays measured vibration data in time waveforms and FFT spectra, complete with alarm levels on the PDA display. A PC-based software program based on Excel is included for use with vibration data exported from the PDA to a PC.

“The Datastick Spectrum software that runs on the PDA places all the vital waveform or FFT spectral information on one screen,” reports Michael Scandling, Datastick’s marketing vice president. “Data can be shown in terms of acceleration, velocity, or displacement.”

Endress+Hauser weighs in with its Minilog B, a 4x4x2.4-in. data logger with two input channels for storing analog and digital values. “It has variable sensor connections using 0/4 to 20 mA, 0-1 V, or Pt100, as well as relay contact for event and pulse counting,” says E+H’s Jerry Spindler. “Alternatively, this input can be used to calculate machine running time. Measured values are updated every second, and it calculates instantaneous, minimum, maximum, or average values. Internal memory can keep 64,000 measured values, or up to 24 hours of recording using a one minute storage cycle.” This one even comes with a small, seven-segment LCD, with decimal point, limit symbols, and battery-life status.