Specifications

Publication 1794-SG002D-EN-P - May 2012
Select FLEX I/O Modules 59
1794-IJ2 and 1794-IJ2XT 24V DC Input Frequency Module
The 1794-IJ2 is essentially a tachometer with the capability of reporting
frequency, acceleration, and direction. Outputs are activated by alarms. Input
devices range from magnetic pickup to flowmeters, to incremental encoders to
proximity detectors. This intelligent I/O module is designed to perform
high-speed frequency algorithms. The module provides 2 frequency inputs,
2 gate inputs, and 2 outputs. The frequency inputs are capable of accepting
frequencies up to 32KHz. The module accepts and returns binary data.
The 1794-IJ2 measures frequency over a user-specified time interval. A frequency
calculation can start before the time interval has elapsed, if a user-specified
number of frequency input pulses have occurred.
The module's primary target is high-speed, accurate frequency measurement. As
such, a high-speed internal clock is synchronized with the frequency input to
count over a user-selected sampling time or a user-defined number of frequency
input pulses.
Power to the module is supplied from the external power supply. All power for
input devices (24V DC) is supplied by the I/O module. Outputs are used to set
alarms depending on the input conditions.
The 1794-IJ2 module accepts the following frequency inputs:
• 24V DC IEC1+ proximity switch as defined by standard IEC 1131-2
• 24V DC contact switch with wire off capability
• 500 mV AC magnetic pickup
• 50 mV AC magnetic pickup
• 6V AC vortex
• 3V AC vortex
The 1794-IJ2 module accepts the following gate inputs:
• 24V DC IEC1+ proximity switch as defined by standard IEC 1131-2
• 24V DC contact switch
• 500 mV AC magnetic pickup
• 50 mV AC magnetic pickup
Customer supplied power, ranging from 10…31.2V DC, is connected internally
to the power output transistor. When an output is turned on, current flows into
the source out of the drain, through the load connected to the ground of the
customer supply (customer return). Diode D6 protects the power output
transistors from damage due to inductive loads. Output Q1 is a thermally
protected FET and will turn off at 3 A (approximately). After an output goes into
thermal shutdown, you must fix the cause of the shutdown and toggle the outputs
ON and OFF to reenergize the output. RT1 protects D6 and Q1 if power supply
polarity is reversed.