QTech Data Systems DNP3 RTU - Manual (Page 15)

DATRAN XL4 RTU – Owners Manual – v1.1 June 2012
www.qtech.co.nz Page 15
channel 8 can be configured as a high speed pulse counter, allowing pulses with duration less than 20 ms to be
detected. Please contact QTech for application specific details.
Note that the digital input status LEDs are controlled by the Q04 Processor and are not connected electrically in
any way with the input circuitry.
The diagram below shows the electronic circuitry of an individual digital input channel. Note that the digital input
channels are each individually opto-isolated. The intention of this design is to prevent noise and voltage spikes
from propagating further into the DATRAN XL4, and has proven to be an effective design.
Circuit details of a Digital Input Channel.
The 4K7 resistor limits the current through the opto-isolator while the 10nF capacitor filters noise from the input line.
The BAV99 prevents input voltage spikes from exceeding the reverse breakdown voltage of the opto-isolator LED.
With a supply voltage of 12V, each digital input channel ON state current to ground is approximately 2.5mA. With a
supply voltage of 24V the current will be approximately 5mA.
The current transfer ratio of the H11A817D opto-isolator is greater than 100%. Therefore a minimum of 1mA must
flow through the opto-isolator LED to ensure reliable switching (assuming a 50% safety margin). This implies that
the maximum allowable ON state resistance of the external switching device is 5k for a 12V supply voltage, and
10k for a 24V supply voltage.
Digital Outputs Digital Outputs Digital Outputs Digital Outputs
The DATRAN XL4 has 8 digital output channels physically separated into two banks. The first bank contains digital
output channels 1 to 4, and is located on the front of the DATRAN XL4. The second bank contains digital output
channels 5 to 8, and is located on the bottom of the DATRAN XL4.
The first bank of the digital outputs has 4 yellow status LEDs to indicate the state of the corresponding digital
output channel. The second bank does not have status LEDs, but in all other respects, operates the same as the
first bank.
In the ON state, the DATRAN XL4 connects the specific digital output channel to ground. In the OFF state a digital
output channel becomes open circuited.
The digital outputs also contains two voltage supply terminals labelled ‘+’ on each bank. These make the internal
switched positive voltage rail available externally. The voltages can be used to deactivate any connected devices if
the DATRAN XL4 goes into low voltage shut down mode.
Note. Relays and other control devices should always be wired to be failsafe. Always ensure that any equipment
attached to relays goes into a safe state when the relay or controlling device is removed or not powered.
The diagram below shows some of the details of the digital output circuit electronics.