Power Over Camera Link
PoCL - Camera Power Distribution
The PoCL controllers are capable of delivering a sustained supply current up to 400 mA to a PoCL compliant camera through a PoCL compliant cable.
Parameter |
Max |
Units |
PoCL camera current rating |
400 |
mA |
The power originates from an external power source attached to the Camera Power connector.
The external power source must be a regulated 12V DC power supply capable of sustaining the current required by the camera(s) and satisfying the voltage requirements of a PoCL frame grabber.
Parameter |
Min |
Typ |
Max |
Units |
Source supply voltage requirement |
11 |
12 |
13 |
V |
Note: The voltage loss across the protection circuits is negligible; the current required by the on-board circuits is also negligible.
PoCL OCP - Overcurrent Protection
The PoCL controllers have an "Over Current Protection circuit": the OCP. It is based upon an electronic device that controls the current delivered to the load using:
- A dV/dt limiter
- A short-circuit current limiter
- An overload current limiter
- A thermal protection
The dV/dt limiter controls the output voltage rising slope. This limits the current during the charging of the load capacitor. The short circuit current limiter is effective when a short circuit event occur. It is also effective during the charging of the load capacitor since during that phase, the load is equivalent to a short circuit.
The overload current limiter is effective during normal operation. The load current increases excessively when the overload level is reached, the overload current limiter will automatically reduce the current to the short circuit level.
The thermal protection limits the temperature of the electronic device by opening the circuit until the device temperature reduces sufficiently.
Following table summarizes the characteristics of the OCP circuit:
PoCL OCP characteristics |
Min |
Typ |
Max |
Units |
Output voltage slew rate |
|
0.15 |
|
V/ms |
Short circuit current limit |
0.6 |
1 |
1.8 |
A |
Overload current limit |
3.1 |
3.2 |
3.5 |
A |
PoCL OVP - Overvoltage Protection
The PoCL controllers have an "OverVoltage Protection circuit: the OVP. It clamps the output voltage in case of a defective external power supply:
PoCL OVP characteristics |
Min |
Typ |
Max |
Units |
Output clamping voltage |
12 |
15 |
17 |
V |
PoCL Device Detector
The PoCL controller has a PoCL device detector, which measures the input impedance of the camera power input circuit at the off state, and checks if it is within the specified limits specified for PoCL cameras.
Therefore, a calibrated sense current is injected by the frame grabber into the power input circuit of the camera through the camera cable. After the expiration of the "sense time delay" time interval that allows the input capacitance to be charged, the detector measures repetitively the voltage during the "sense OK time". If the voltage stays between the limits, the power is applied.
The camera must deliver a clock within the "initial clock turn-on delay" after the application of the power. If this is not the case, the frame grabber turns off the power immediately.
While the camera is powered, the PoCL device detector monitors continuously the Camera Link clock. If this clock is interrupted during at least "turn-off delay after clock loss" time interval, the power is immediately turned off.
PoCL device detector characteristics
|
Min |
Typ |
Max |
Units |
Sense current on 10K impedance load |
30 |
52 |
75 |
ľA |
Detector thresholds |
0.3 |
|
1.2 |
V |
Allowable impedance range |
8 |
10 |
12 |
kΩ |
PoCL camera detector sense time delay |
|
500 |
|
ms |
PoCL camera detector sense OK time |
|
500 |
|
ms |
Initial clock turn-on delay |
|
500 |
|
ms |
Turn-off delay after clock-loss |
|
500 |
|
ms |