Technical Description; Features - SeaLevel ISO-16.PCI User Manual

The ISO-16.PCI provides two parallel input ports. Port A and B are interfaced to optically isolated inputs.
Assuming an I/O address of 300 Hex the following table shows the Port Addresses.
Base Address
Port A Address
Port B Address

Features

•
2 eight bit input ports
•
DB-37 female connector
•
Multiple adapters can reside in same computer
Ports A and B are 8 bit input ports connected to optically isolated input sensors. Each sensor can be used to
interface a voltage input and then sense whether the voltage is on or off. Each sensor is isolated with respect to a
common ground from every other sensor and also isolated with respect to the host PC ground. This means that
signals such as low-level AC voltage, motor servo voltage, and control relay signals can be 'sensed', or read by the
PC, without the risk of damage due to ground loops or ground faults.
Each sensor input pair has a current limiting resistor that is used to limit the input current to the opto-isolator. The
opto-isolator has two 'back-to-back' diodes internally. This allows AC or DC signals to be sensed regardless of
polarity. When the signal is high enough to cause the opto-isolator to turn-on, the output of the opto-isolator goes
low (0 volts) and the port bit is read as a low logic level (binary 0) by the PC. When the input signal is too low to
turn on the opto-isolator, the output goes high and the port bit is read by the PC as a high logic level (binary 1).
The input impedance of each isolated input is approximately 560 ohms (factory default). The opto-isolator requires
approximately 3 mA to turn on. The maximum input current is 60 mA. There are two things to consider when
selecting the input resistor. The first is turn on voltage for the circuit to sense, and second is the maximum input
voltage. Maximum input voltage must not provide too much power to the input resistor, and must also not overdrive
the opto-isolator input current specification. The following formulas apply:
Turn on current: 3 mA
Isolator diode drop: 1.1 V
Resistor power Max: .25 W
Turn on voltage = diode drop + (turn on current) x (resistance)
Or :
1.1 + (.003) x R
Maximum voltage = square root of (.25 (resistor value))
The following table shows four common input resistors, the range of voltages, and maximum current associated
with each.
Input Resistor
(Ohms)
220
560
1K
2.2K
Increasing the input resistor accordingly can increase the maximum input voltage. Because socketed DIP resistor
networks are utilized, they can be replaced with a different value. This can be done at the factory, if necessary.
Sealevel Systems ISO-16.PCI

Technical Description

Hex Decimal
300 768
301 769
Min Turn-On Max Input Range
(Volts) (Volts)
1.76
2.8
4.1
7.7
Technical Description
Mode
Input Port
Input Port
Max Current
(mA)
7 27
12 20
16 15
24 10
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