User manual

Page 30 915U-2 Wireless I/O
Page 30 User Manual
2.5.4 Pulsed Inputs
The 915U-2 supports 8 x digital signals, of which inputs 1 to 4 can be used as pulsed
inputs.
The maximum pulse frequency is 50 KHz for Input 1 & 2 and 1 KHz for Input 3 & 4.
Digital/Pulsed inputs are suitable for TTL signal Level, NPN-transistor switch devices or
voltage-free contacts (relay/switch with debounce capacitor).
Voltage Free Contact
Transistor
Switch Device
V+
V-
DIO1
DIO2
GND
915U-2
DIO3
TTL CMOS
Output
Figure 14 – Pulsed Input Wiring
Frequencies greater than 1 KHz need to use a TTL logic drive or an external pull-up
resistor (1KΩ to V+). Pulsed inputs are converted to two different values internally. First
is the Pulse Count, which is an indication of how many times the input has changed
state over a configured time period. Secondly there is a Pulse Rate which is an analog
input derived from the pulse frequency. E.g. 0 Hz = 4mA and 1 KHz = 20mA.
All Pulsed Input counts are stored in non-volatile Ram so in the event of a power fail or
the module being reset the values will be saved.