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PC/104 A/D I/O card spans wide temperature range

Posted: 11 Apr 2006 ?? ?Print Version ?Bookmark and Share

Keywords:PCM-MIO? I/O card? WinSystems? Alex Mendelsohn?

PCM-MIO I/O card

At last week's Embedded Systems Conference, board maker WinSystems rolled out its PCM-MIO, a high-density analog and digital PC/104-compliant I/O card. The PCM-MIO operates from -40C to 85C. It's supplied with free drivers for Linux, Windows CE, Windows XP Embedded and ROM-DOS.

The PCM-MIO includes a 16-channel 12bit ADC, and an 8-channel 12bit DAC. It also packs 48 lines of digital I/O.

Quad DAC chips
The DAC circuits are based on two Linear Technologies SoftSpan quad DAC chips. They're software-programmable for either unipolar or bipolar operation, plus specific voltage range on a per-channel basis.

These chips tout integral nonlinearity and differential nonlinearity to 1 LSB over the temperature range in both unipolar and bipolar modes. The SoftSpan devices also include internal de-glitcher circuits that reduce glitch impulses to less than 2nV.

Uni- and bipolar I/O
Analog input ranges for the PCM-MIO card are 0-5V, 5V, 0-10V, and 10V. The board will support up to 16 single-ended or eight differential input channels, or various combinations of both. It's also available with either 12bit or 16bit ADCs.

DAC output voltage ranges are 0-5V, 0-10V, 5V, and 10V.

One of the most salient features of this card, aside from its very wide temperature range, is its lack of trimmer potentiometers for calibration of its analog circuitry. No on-board pots to adjust results in quick setup of analog systems that require accurate digitally-controlled voltages.

This feature also eliminates the need for a technician or field engineer to re-adjust or re-calibrate the unit.

According to WinSystems, the analog section of its board has also been designed with ultra-low-noise power supplies and a low-drift voltage reference. These factors are critical for accurate measurements up to 16bit resolution.

Low-noise supplies
Included on the card is a low-noise 15V power supply based on a Linear Technologies LT1533 switching regulator chip. It helps reduce both conducted and radiated EMI, which is achieved by independent control of voltage and slew rates for both positive and negative voltages.

A separate regulator on the PCM-MIO is used to generate an analog 5V supply for the data converters. This is done to minimize digital switching noise, since converters inherently have low power supply rejection ratios. The result is less than 300?V p-p noise from DC to 1MHz on all analog supply voltages.

Special layout techniques and low-drift resistor networks are also used to maintain precision, accuracy, and long-term stability. In operation there are no missing codes, and measurements are monotonic over the product's full temperature range.

Use with signal conditioners
WinSystems' PCM-MIO is compatible with isolated signal conditioners that will protect, filter and isolate the analog input and output signals from electrical transients. There are many models available from third-party vendors to interface to a variety of voltage, current, temperature and position sensors, as well as analog-based instrumentation.

The PCM-MIO is compatible with Dataforth's SensorLex 8B Isolated Signal Conditioners. These modules are designed to protect, filter and isolate input signals from electrical transients and industrial equipment power-line voltages, while reducing electrical noise in measured signals.

There are many models to interface to voltage, current, temperature, position, frequency, and strain measuring devices. The SensorLex 8B line of analog signal conditioners come in 15 family groups with a total of 95 models.

Programmable digital I/O
Back to the PCM-MIO card. Its 48 lines of digital I/O are individually programmable for input, output, or output with read-back. All lines are TTL-compatible and can source and sink 12mA. That permits direct connection to industry-standard optically-isolated AC and DC signal conditioners.

The PCM-MIO measures 3.6-by-3.8 inches in size (90-by-96mm).

Price is about $395. Delivery is stock to three weeks.

- Alex Mendelsohn

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