Publication 1794-6.5.11 - November 1997
How Communication Takes Place and I/O Image Table Mapping with the DeviceNet Adapter
5
-5
Bit/Word Descriptions
for the Frequency Input Module (1794-IJ2)
Word
Bit
Definition
Read
Word 1
Bit 00-15
(00-17)
Calculated value of Frequency (channel 0) – Frequency can be reported down to 1 or 1.0 Hz, depending on the Frequency
Range bit setting; below a 1 Hz value, 0 is reported; below a 1.0 Hz value, 0.0 is reported. Calculated frequency depends on
Minimum Sampling Time and Missing Pulse Multiplier.
Word 2
Bit 00-15
(00-17)
% of Full Scale or Acceleration (channel 0) – Value of the calculated Frequency scaled by the Maximum Frequency, or
Calculated Value of Acceleration in Hz / second, depending on the state of the Freq or Accel Alarm Select bit. Note: % Full
scale will be calculated accurately up to a maximum of 3,276.7%. Beyond this maximum, the value of 3,276.7% will be
returned, and a “Calculation Failure” (9) will be set in the Diagnostic Status byte.
Word 3
Bit 00-15
(00-17)
Calculated value of Frequency (channel 1) – Frequency can be reported down to 1 or 1.0 Hz, depending on the Frequency
Range bit setting; below a 1 Hz value, 0 is reported; below a 1.0 Hz value, 0.0 is reported. Calculated frequency depends on
Minimum Sampling Time and Missing Pulse Multiplier.
Word 4
Bit 00-15
(00-17)
% of Full Scale or Acceleration (channel 1) – Value of the calculated Frequency scaled by the Maximum Frequency, or
Calculated Value of Acceleration in Hz / second, depending on the state of the Freq or Accel Alarm Select bit. Note: % Full
scale will be calculated accurately up to a maximum of 3,276.7%. Beyond this maximum, the value of 3,276.7% will be
returned, and a “Calculation Failure” (9) will be set in the Diagnostic Status byte.
Word 5
Bits 00
Missing Pulse Alarm (channel 1) – Indicates when no Frequency input pulse has occurred within the period determined by the
Minimum Frequency Sampling Time and the Missing Pulse Multiplier. Primary control is given to the Missing Pulse Multiplier
to determine when this bit is set. However, if the Missing Pulse Multiplier is set to 0, then the Minimum Frequency Sampling
Time characteristics will determine when this bit is set.
Bit 01
Wire Off Fault Alarm (channel 1) – when set, indicates when 24 Vdc Input (IEC 1+ or Switch Contact with shunt) Wire Off
Detection has gone true for any of the Frequency or Gate inputs on a channel that has the Wire Off Fault
Select = 1.
Bit 02
Frequency or Acceleration Alarm (channel 1) – Changes state from 0 to 1 if the calculated Frequency (actual or scaled)
exceeds the user programmed Maximum Frequency, or the absolute value of calculated Acceleration/Deceleration exceeds
the user programmed Maximum Acceleration Value.
The Frequency Alarm turns off when the Frequency drops below 95% of the Alarm Value.
The Acceleration Alarm turns off when the Acceleration drops below 90% of the Alarm Value.
Bit 03
Gate Input State (channel 1) – Indicates if there is a valid signal on the gate input. This parameter is only determined once
every 0.5 – 2s.
Bits 04-05
Direction (channel 1) – Indicates the current Direction of Rotation, using both the Frequency and Gate inputs. (Frequency
leads Gate = Clockwise, Gate leads Frequency = CounterClockwise). Used for slow speed detection from 1 – 1,500Hz. “No”
or “Stopped” rotation can be determined by the state of the Missing Pulse Alarm, when it is switched on. A missing
Frequency Input will generate a Missing Pulse Alarm, a missing Gate Input will only generate a “No Sensor Present /
Detected” status (3).
Bits 06-07
Not used
Bits 08 (10)
Missing Pulse Alarm (channel 0) – Indicates when no Frequency input pulse has occurred within the period determined by the
Minimum Frequency Sampling Time and the Missing Pulse Multiplier. Primary control is given to the Missing Pulse Multiplier
to determine when this bit is set. However, if the Missing Pulse Multiplier is set to 0, then the Minimum Frequency Sampling
Time characteristics will determine when this bit is set.
Bit 09 (11)
Wire Off Fault Alarm (channel 0) – When set, indicates when 24 Vdc Input (IEC 1+ or Switch Contact with shunt) Wire Off
Detection has gone true for any of the Frequency or Gate inputs on a channel that has the Wire Off Fault
Select = 1.
Bit 10 (12)
Frequency or Acceleration Alarm (channel 0) – Changes state from 0 to 1 if the calculated Frequency (actual or scaled)
exceeds the user programmed Maximum Frequency, or the absolute value of calculated Acceleration/Deceleration exceeds
the user programmed Maximum Acceleration Value.
The Frequency Alarm turns off when the Frequency drops below 95% of the Alarm Value.
The Acceleration Alarm turns off when the Acceleration drops below 90% of the Alarm Value.