VC20XX Operating Manual
32
8.1.2 Shutdown Function for VC20XX Smart Cameras
VC20XX Smart Cameras incorporate a circuit to detect and protocol power failures. If the PLC
output power supply (12-24V PLC, Pin 1 and 9) of the cameras is interrupted, the system
variable “POWFAIL” is set to “1”. In case the PLC outputs are supplied, the status of
“POWFAIL” is “0” (refer to the sysvar.h).
This behaviour, that can also be checked using the shell command “ht”, can be used to perform a
controlled camera shutdown in case of a power failure.
Connecting the PLC/ Power interface for using this feature:
Signal
Pin No.
color
connect to
24V IN Cam
2
red/blue
24V backup supply (supplying power at least 100ms
longer than grid supply in case of a power failure)
24V PLC
1
red
24V standard power (grid) supply
24V PLC
9
grey/pink
24V standard power (grid) supply
GND IN com.
3
black
GND power supply
Here, the PLC voltage (24V PLC) is connected directly to the power (grid-) supply. The main camera
power supply at Pin 2 should remain high for at least 100ms longer than the power supplied to the
PLC supply. This can be done for instance with help of a suitable capacitor.
If a power failure occurs or if the main power supply is turned off, the camera detects this signal not
being present and the POWPLC status is changed from 0 to 1.
The system variable can be polled from time to time using the getvar(POWFAIL) function. This can be
best done using a background task.
The following procedures can be performed:
1. Stopping the operation of all programs and interrupts (no pictures will be taken any longer).
2. Saving all buffers (to multi-media card or flash EPROM).
3. Protocol time and date of the shutdown.
4. The procedure then waits for the backup voltage to disappear or main power to re-establish. If the
latter happens the program might be able to continue where it has stopped. (In this case there
may be some lost images = some parts not checked correctly)
Note that this feature is for emergency use only and is not designed to handle frequent
interruptions. The backup voltage must be able to supply the specified voltage for a period of
at least 100 msec (in addition to the polling delay).
!
24V PLC
GND
to camera
24V PLC
GND
24V backup
from power supply
capacitor
10000
µ
F
Sample Circuit for using the “power fail detect shutdown function”
©
1996-2007 Vision Components GmbH Ettlingen, Germany
VC20XX_HW.pdf
