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Isolated input with relay output

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article image Low-cost, half-size PCI card.
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THE PCI-DIO8 from Interworld Electronics is a low-cost, half-size PCI card that provides isolated input and relay output for PCI-Bus computers.

The card has eight optically-isolated digital inputs for ac or dc control signals and eight electromechanical relay outputs. PCI-DIO8 occupies four consecutive eight-bit registers in I/O space.

The isolated inputs can be driven by either ac or dc and are not polarity sensitive. Input signals are rectified by a diode bridge and applied to inputs of opto-isolators. A 470W resistor in series provides current limiting. Standard 12/24 ac control transmitter outputs can be accepted as well as dc voltages. The input voltage range is 5V to 24V (rms). To extend the input voltage range, external resistors may be connected in series.

Each input circuit contains a switchable slow/fast filter that has a 10-millisecond time constant. (Without filtering, the response is 20 microseconds.) The filter must be selected for ac inputs in order to eliminate response to zero crossings.

The filter is also valuable for use with slow dc input signals in a noisy environment. The filter may be switched out for dc inputs in order to obtain faster response. Switches on the card individually select the filters or they may be globally controlled by software.

Interrupts are enabled/disabled by software. When the change-of-state detection circuit is enabled, the card asserts an interrupt whenever one or more of the interrupts changes state. Once an interrupt has been generated and serviced, it must be cleared by system software.

The electromechanical relay outputs are comprised of five Form C SPDT outputs and three Form A SPST (normally-open) type. The relays are all de-energised at power-on. In addition, data to the relay is latched.

PCI-DIO8 utility software provided on CD includes an illustrated setup program and sample programs in QuickBASIC, Pascal, and C. The sample programs sequentially turn on each relay until all are on and then sequentially turn them off.

After each relay is turned on, the relay states are read back, the opto-isolated input are read, and the data is displayed. Interworld Electronics 03 9563 5011.

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