5. USER INTERFACES
5.11.3
12-bit I/O (AI, DI, DO) Port
The 12-bit I/O port user interface (also referred to as CNT port – counter) is used to monitor
analog and binary input signals and to control binary output signals. The interface has 6 inputs
and 1 output. Two of the inputs can be configured as binary counter inputs or general purpose
binary inputs. There are also 2 dedicated binary inputs, 2 analog current inputs, and 1 open-
collector output. The options for the I/O port are configured by writing to register values on the
I/O board using the
MODBUS ASCII
protocol.
The unit can periodically store the values of the inputs in memory. These log entries can
be read by reading the individual memory locations. Up to 224 log entries may be stored. The
logging interval can range from 1–65535 minutes.
Analog Inputs
The analog current inputs have a range from 0 to 20 mA. The input impedance is 100
Ω
and the ADC resolution is 12 bits. The averaging and sampling period may be adjusted by the
user. Also, alarms thresholds may be set for each input. The ADC value stored in memory is
calculated using the following equation:
ADC Value = ((12b value + addit. constant) * multiplic. constant)/1000
where the constants are programmed into memory by the user.
Binary Input
The binary input is sampled 8x per second with a sampling period of 1/64 seconds. The
active level for each binary input may be set to either a logic 0 or logic 1. The inputs may be
configured to generate an alarm when they become active. The input threshold for detecting
a logic 1 can be set at either 8 uA or 20 mA using a jumper on the module board.
Counter Input
The counter inputs have a maximum input frequency of 100 Hz. The minimum input pulse
width is 1 ms. The counter input may be configured to generate an alarm when a threshold is
reached.
Binary Output
The binary output is a transistor with an open collector output. In the inactive state (logic 0)
the transistor is off. In the active state (logic 1), the transistor is on and will connect the output
signal to ground (GND). The output transistor is rated at 100 mA and 30 V.
The output may be configured to generate a pulse from 125 to 8000 ms in length. It is also
possible to configure the unit so that the output will become active when counter 1 (CNT1)
reaches a threshold.
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