DESCRIPTION AND OPERATION
SECURITY FUNCTIONS
I-E96-215A
2 - 3
Analog Inputs/Outputs
There are four analog inputs and two analog outputs on-board.
The inputs must be 1 to 5 VDC analog signals. The outputs are
dipswitch selectable to be either a voltage signal (1 to 5 VDC) or
a current signal (4 to 20 milliamps). The I/O signals are routed
through the same termination unit and cable as the digital I/O
signals.
Digital Control Station Serial Link
Communication between the QRC and a digital or analog con-
trol station is via a five kilobaud, RS-422 serial link. A maxi-
mum of four stations can be daisy chained on the serial link.
SECURITY FUNCTIONS
Two types of security functions are performed: module security
and control input security. Module security is provided by a
machine fault timer (MFT) that is periodically reset by the
microprocessor. If the timer is not reset, it:
•
Shuts the module down.
•
Turns the front panel status LED red.
•
Causes the analog outputs to either hold, go to 0 percent,
or go to 100 percent (user-selectable).
•
De-energizes the digital outputs.
•
Prevents writing to or erasing the NVRAM.
Control input security is provided by adding function code 31
(test quality) to the configuration. This function tests the qual-
ity of a maximum of four inputs. If the inputs are good, the out-
put of the test quality block is set to Logic 0. If any of the
inputs are bad, the output of the block is set to Logic 1.
Depending on the importance of the input, the block output
can cause transfer of control to a manual/auto station, shut
down the process or send a warning to the user.
Additionally, on-line tests are performed to verify proper hard-
ware operation. If any of these tests fail, the timer is not reset
and status LED turns red. If an NVRAM checksum error is
detected, the module continues operating; however, the status
LED flashes green. After resetting the module, it will enter the
error mode.
