CCTV Articles

PT-3 Female DC Plug

The PT-3 Female DC plug is one of the many standard components of a digital video security camera system.  There are several standard electrical, or rather, power, components that are used to supply the cameras with the proper amount of power.  Let’s take a look at a digital video security system and see how it works and how the PT-3 Female DC Plug is used.


A digital video security system consists of three basic components; one or more digital video cameras, a Digital Video Recorder or DVR, and one or more display monitors.  The digital video camera “captures” (transfers, sees, or records) video image data which it sends to the DVR.  After a certain amount of processing, the DVR records and/or displays the data as a digital video that can be seen on one or more monitors.


Now we’ll take a closer look at how the digital video camera works and the relationship of the PT-3 Female DC plug to the camera.


The digital video cameras primary function is to capture an image created by the reflection of light rays and transform it into electrical data that can be used to create the exact same image electronically, as on a monitor or television.  Also, since the camera does create electronic data, it should be able to be compiled and used to create a digital video file that can be stored and viewed at a later time.


The camera functions by using a lens to focus a field of view area (what the camera is currently looking at) onto a small sensor chip.  The sensor chips usually range in size from 1/4 to 1/2 inch square although probably the most common ships used are the 1/4″ and the 1/3″ square chips.


There are two different type of sensor chips.  They both produce the same basic end result but each one goes about producing that result in a different manner.  The two different chips are either a Charged Coupled Device or CCD or a Complementary Metal Oxide Semi Conductor or CMOS.


When the focused light image strikes these sensor chips it causes electrical impulses to be produced from the sensor.  These impulses can be measured and are used to create electronic data that can produce a digital photograph or digital video image.  Advanced technology has produce CCD and CMOS chips that, at one time may have had measurable differences, but now are basically the same.


Once the electrical impulses are created and measured they are processed by an on-board analog-to-digital processor chip that converts the analog signal into a digital format.   The digital information is then processed by a Digital Signal Processor or DSP.  The DSP makes adjustments and add the finishing touches to the data before sending the it along as a digital video transmission signal, usually along RG-59 coaxial cable to the DVR and/or monitor.


All of this electronic work does not occur “for free.”  Power must be provided to the camera in order for the sensor, Integrated Circuit (IC) chips, and transmitters to work properly.  This is where the PT-3 Female DC plug comes in.


Most digital video cameras today work on either 12 Volts Direct Current (VDC) or 24 Volts Alternating Current (VAC).  The PT-3 Female DC plug is designed to work with the 12 VDC systems only (and not the 24 VAC systems).  Since DC voltage travels in one direction, there is a positive and a negative connection.


The PT-3 Female DC plug is a 2.5 mm female type cylindrical plug.  The outer area of the plug is actually a metal contact and inside the cylinder is an isolated metal pin that is the other metal contact.  Although polarity can be reversed by simply switching the connection wire around, the center conductor is normally designated as the positive conductor while the outer metal sheath is the negative conductor.


The PT-3 Female DC plug is also the standard type connector for all 12 VDC digital video cameras.  If polarity rules are followed when connecting the power leads from the plug to the power supply wires, connection to the camera is a snap; all that is required to connect the power is to plug the connector into the camera’s male receptacle.


The one, most important concept that cannot be stressed enough when using a PT-3 Female DC plug is to make sure that polarity rules are followed being certain that the center pin of the female plug is connected to the positive power lead.


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