Optical Isolation Circuitry; Digital Filtering - National Instruments DAQ 6527 User Manual

Optical Isolation Circuitry

Digital Filtering

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• Input ports
– Read
– Apply digital filtering (software programmable)
– Detect changes on selected lines (software programmable)
Table 3-1, Port Functionality for 6527
functions.
The digital input ports of a 6527 device are optically isolated using Infineon
IL55B optocouplers. Each IL55B provides optical isolation for one channel
of input.
Isolation on the output is provided by Infineon LH1546 solid-state relays.
One solid-state relay is used for isolation at each channel of output.
For diagrams of the complete input and output circuitry, see Chapter 3,
Signal Connections.
All of the inputs on the 6527 device contain a digital filter option. Filtering
can help eliminate glitches on input data. When used with change
notification, filtering can also reduce the number of changes for you to
examine and process.
You can configure any of the digital input channels from the optocouplers
to pass through a digital filter. You can also control the timing interval used
by the filter. The filter blocks pulses shorter than the specified timing
interval, treating them as glitches. The filter passes pulses longer than twice
the specified interval. Intermediate-length pulses—pulses longer than the
interval but less than twice the interval—may or may not pass the filter.
The filter operates on the inputs from the optocouplers. The optocouplers
turn on faster than they turn off, passing rising edges faster than falling
edges. The optocouplers can therefore add up to 100 µs to a high pulse or
subtract up to 100 µs from a low pulse (a 100 µs change is typical at
I = 5 mA, RL = 100 ). As a result, the pulse widths guaranteed to be
F
passed and blocked are those shown in Table 4-1.
Devices, contains a summary of port
4-3
Chapter 4 Device Overview
6527 User Manual