Power over Camera Link

The PoCL controllers of Grablink cards fulfills the requirements of the Power over Camera Link (PoCL) as specified in section 4 of the Annex E of the Camera Link Standard v2.1 for Switchable PoCL SafePower frame grabbers, namely;

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SafePower Switchable power output to allow the frame grabber to operate safely with PoCL and non-POCL cameras.

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Automatic detection of PoCL cameras

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Capable of supplying up to 4W of power to the camera through each Camera Link connector

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Over-current protection (OCP)

In addition, it provides the user with:

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an AUTO/OFF control through the PoCL_Mode parameter.

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a PoCL status through the PoCL_Status parameter.

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on 1621 Grablink Express only, a shield-to-ground switch control through the PoCL_GroundJumper parameter.

PoCL Controller Unit Specification

Parameter	Min.	Typ.	Max.	Unit
DC input voltage requirement	11	12	13	V
DC output voltage @ON-state	11	12	13	V
PoCL power output	4			W
PoCL current rating	400			mA

Power Source Requirements

The power originates from an external power source that has to be attached to the Camera Power Connector for 1621 Grablink Express or to the Power Input Connector for 1624 Grablink Base, 1623 Grablink DualBase and 1626 Grablink Full XR.

The external power source must be a regulated 12V DC power supply capable to sustain the current required by the camera(s).

Note: The voltage loss across the PoCL Controller Unit and its own power consumption are negligible.

Note: For 1623 Grablink DualBase and 1626 Grablink Full XR, the power source is common for both PoCL controllers.

Power Output Capabilities

A PoCL controller is capable to deliver a sustained supply current up to 400 mA to a PoCL compliant camera through a single PoCL compliant cable. Assuming a minimal supply voltage of 11 VDC and a voltage loss of 1 V in the cable, a PoCL camera can safely drawn a maximum of 4W of power through each Camera Link cable.

Applies to:

When a PoCL Camera Link Medium, Full or 80-bit camera is attached to 1626 Grablink Full XR, the power can be delivered through any one or both cables according to the results of the PoCL device detection performed by each PoCL controller.

Cameras that draw less than 4W may draw power from only one connector, usually the Base Camera Link connector.

Cameras that draw more than 4W must draw power from both connectors. In addition, such cameras must satisfy the following requirements:

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The camera's power supply shall be designed so that it does not draw more than 4W per cable.

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The camera's power supply shall be designed to isolate the two Camera Link connectors, i.e. power applied to one connector shall not be injected into the other one.

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The camera shall implement a voltage detection circuit that only enables the camera's power supply when power is present on both Camera Link cables.

When a PoCL Camera Link Base camera is attached to 1626 Grablink Full XR, the power is delivered through a single cable attached on the Base Camera Link connector. Only the PoCL controller #1 is delivering power, the controller #2 remains in the "Disconnect" state.

Each PoCL controller embeds an overcurrent protection circuit - OCP - based upon an electronic device that controls the current delivered to the load using:

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A dV/dt limiter

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A short-circuit current limiter

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An overload current limiter

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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 when 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.

OCP Characteristics

Parameter	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

Each PoCL controller integrates an overvoltage protection circuit - OVP - that clamps the output voltage in case of a defective external power supply.

OVP characteristics

Parameter	Min	Typ	Max	Units
Output clamping voltage	13	15	17	V

Each PoCL controller implements a PoCL device detector that measures the input impedance of the camera power input circuit at the off state and check if it is within the specified limits specified for PoCL camera Link 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 thresholds, 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

Parameter	Min	Typ	Max	Units
Sense current on 10K impedance load	30	52	75	µA
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

Current Capacity for PoCL Cables

Camera Link Standard (version 2.0) requires that the power and drain wires within a cable assembly shall be capable of handling 1.0 A camera current under fault conditions. The power and drain wires shall be at least AWG 28 or larger diameter.

Conductor Resistance for PoCL Cables

Camera Link Standard (version 2.0) requires that the DC resistance of any power wire or drain wire shall not exceed 2.5 Ω for the length of the cable assembly.

Note: The overall voltage drop on the loop is 1.0V ensuring at least 10V at the camera side for the minimal supply voltage of 11 V.

Considering that AWG 28 conductors have a typical resistance per unit length of 0,21 Ω/meter, cables using this wire gauge satisfy the above requirements for cable lengths up to 11 meters.

Note: The 10V minimal voltage requirement at the camera side can be satisfied with longer cables if the minimal supply voltage is higher than 11 V or if the camera draws less than 400 mA.

To avoids unexpected activation of PoCL when the camera is not powered trough the Camera Link cable:

1.

Before Channel activation: set PoCL_Mode to OFF

2.

Set ChannelState to READY