Saturday, November 23, 2013
This diagram illustrates the general layout of the most common type of CCD array, the Interline Transfer CCD. The CCD is composed of precisely positioned light sensitive semiconductor elements arranged as rows and columns. Each row in the array represents a single line in the resulting image. When light falls onto the sensor elements, photons are converted to electrons, the charge accumulated by each element being proportional to the light intensity and exposure time. This is known as the integration phase. After a pre determined period of time the accumulated charge is transferred to the vertical shift registers.
In cameras conforming to the video standards mentioned above the charge transfer to the vertical shift registers is accomplished in two stages. Initially the charge in the odd numbered rows is transferred, followed by the even rows. Next the charges in the vertical registers are shifted into the horizontal shift register and clocked to the CCD output. Consequently all the odd rows are clocked out first (odd field) followed by all the even rows (even field). The rate at which the charge from the horizontal shift registers is clocked out is governed by the number of elements (pixels) per row and the video standard the camera complies with.
An inherent problem associated with the interline transfer CCD lies in the fact that the vertical shift registers running across the array are insensitive areas and as such act as blind spots. One way of overcoming this is to fabricate micro lenses over each element thereby increasing the effective area of the cell. The lenses also help with the smaller format CCD. Because of the electrical characteristics of the semiconductor substrate on which the CCD is formed each cell has an absolute minimum separation from adjacent cells. Therefore smaller CCDs require smaller cells. Reducing cell size reduces the amount of accumulated charge, using lenses increases the incident light.
Another way of overcoming the problem caused by the vertical shift registers is to do away with them and utilize a different charge transfer mechanism. Frame Transfer CCDs do exactly that. This type of CCD has a separate storage area into which the charge is directly transferred from each cell. This process has to be performed rapidly in order prevent blurring as transfer occurs during the exposure time. Once in the storage area the charge can be clocked out in a similar manner to the interline transfer device.
Thursday, November 7, 2013
Splice the Wires for a Security Camera
For Power Supply Cable:
Security cameras need two types of cables to operate.
1. Power supply cable and
2. Video cable.
Wireless security cameras do not require a video cable but they do require the power supply cable. The power cable transports 12V DC, low-voltage power from the transformer, which is plugged into an 220VAC ~ 110VAC power outlet, to the camera. This cable has two 18 gauge wires, a positive wire and a negative wire, both inside a single jacket. The negative wire will be marked with a black or white stripe. The video cable is a RG-59 / RG6 / RG11: coaxial cable which is shielded and requires BNC connectors to protect the integrity of the video signal being carried.
Use your knife or cable cutters to split the two insulated wires apart approximately three inches from the cut end of the cable, leaving the installation intact on both wires. You can usually pull these apart with your hands. Do this on both ends which you intend to splice together. You should now have two power cables, with two insulated wires coming out of each for a total of four wires to be spliced.
Remove half an inch of the insulation from the end of each of these four wires.
Splice these two power cables together, using wire nuts, by twisting the exposed copper ends together making sure that you twist positive from one cable to the positive from the other cable and the negative wire, or striped wire, from one cable to the negative wire, or striped wire, from the other cable. Screw a wire nut on to the joined or twisted together positive wires and a second wire nut on the twisted together negative wires. Lay the wire nuts against the cable and wrap everything with insulated electricians tape.
Splice these two power cables together, using Butt connectors, by preparing the cables just like you did for the wire nut splice, only without twisting them together. Insert the exposed copper wire from the positive conductor into one end of the butt connector and crimp that end of the connector down. Insert the other positive wire into the other end of the same butt connector and crimp it down. Do the same for the two negative wires using a second Butt connector. Wrap everything with insulated electricians tape.
For Video Cable:
Look at the cut end of the RG-59 cable and you will see four separate parts which make up this cable. In the center is the copper center conductor wire. Surrounding the center conductor wire is a polyurethane white insulator. Next is the aluminum or copper braid. And finally, there is the outer jacket of the cable. As you prepare this cable for the BNC connector is important that you prepare each of these four separate parts independently of each other. The copper center conductor must remain untouched by the braid.
Take the BNC crimping tube and hold it alongside the end of the RG 59 cable to measure your first cut. The crimping tube will have a larger diameter part and a smaller diameter part. The larger diameter part is the end of the crimping tube that you want to match against the end of the RG-59 cable.
Mark, or just eyeball, the outer jacket on the cable where the large part of the crimping tube ends and the smaller part begins. This will be about 3/8 or 1/2 inch from the end of the cable. This measurement depends on the length of the large part of the crimping tube which you have purchased with the BNC connector.
Cut and remove the outer jacket only by ringing it with a pocket knife or using cable cutters. Be very careful not to damage the aluminum braid which is right underneath the outer jacket.
Unravel the exposed aluminum braid so you can pull it away from the polyurethane insulation around the copper center conductor.
Cut and remove the polyurethane insulation from the copper center conductor. You can ring it with a knife or use cable cutters and it should pull free towards the cut end of the center conductor. The cable is now ready for the connector and the cable should now have only the copper center conductor exposed and the aluminum braid pulled back over the outer jacket.
Slide the crimp tube over the cable with the small end going on the cable first. Before you can slide the crimp tube on you must pull the aluminum braid towards the cut end of the cable so the crimp tube can go around it and slide directly onto the outer jacket of the cable.
Slide the BNC connector into place, small end first, with the copper center conductor and the polyurethane insulation going inside of the small part of the connector and the aluminum braid and outer jacket staying on the outside of the small part of the connector. As you push the connector down into the cable it will pull the aluminum braid down inside the outer jacket at the same time. Looking inside the connector and make sure that none of the aluminum braid has inadvertently remained inside the connector and possibly touching the center conductor. If the aluminum braid is touching the center conductor the connection will not work.
Slide the crimping tube back up the outer jacket until it is touching the BNC connector. Use your crimping tool to now crimp the larger portion of the crimping tube and complete the compression placement of the BNC connector.
Repeat this process, placing the second BNC connector on the second piece of cable. When you have completed this you should have two pieces of video cable with a BNC connector on each piece. Use the BNC barrel connector to connect these BNC connectors together. The video cable splice is now complete.
Tuesday, November 5, 2013
Wire and cable fault location equipment has rised as a result of cable applications, using the progress and development of electronic technology, after having a century of changes, the key still but looks Nisshin. As a result of few cable systems failure, positioning experience accumulate very slow. Using the use of automation, technology, the instrument has made substantial progress. Power Cable Fault Locator is utilized to do this work. There are four steps of cable fault location process.
(1)CABLE FAULT TYPE JUDGMENT
Should first serious take a look at the failure of cable throughout, fully understand the faulty cable, and detailed records, which will help find fault faster. Positioning method and sort of cable fault. Judgment cable fault type enables you to measure the insulation resistance or DC voltage test. Shaking table or digital megger relative measurement fault cable and white, and metal outer sheath-ground insulation resistance value. Point of failure the measured worth of the insulation resistance measuring voltage, the condition of the environment, sometimes values ??vary greatly. At different voltages, to see the changes over time, the insulation resistance of the fault point, combined with the characteristics from the cable and laying path, so that you can interpret many of information, as an example, the sort of failure as well as the possible positions.
Bridge method and wave reflection way of the the pretargeting two main means. The proportion of resistance on the point of failure on sides of the cable core resistance and instrument constitutes the Murray Bridge, can be a traditional classic cable fault location. Positioning the bridge equipment low cost, simple operation, and had widespread use. Traditional positioning from the bridge, the rated output voltage only 500V, unable to locate high impedance fault. The big quantity of applications, cross-linked polyethylene cable breakdown is difficult to form the conductive zone breakdown point resistance is high, or even have the ability to withstand our prime voltage was flashover type breakdown. Using the positioning of the popularity of wave reflection method, the method of application of the bridge gradually reduce, not known towards the new cable users.
The precise positioning ahead of the point of failure, you need to know the position and direction of the underground cable, the relevant details are often inaccurate, not even. With a dedicated path analyzer measured to find the position and direction of the underground cable. Path analyzer uses the audio induction method to appraise the cable path. The audio generator for the the measured cable input audio signal current on the headend, the receiver is received on a lawn fault cable generates a magnetic signal to its path and depth measurement.
Depending about the kind of fault, there are various ways and instruments for pinpointing. Cable Fault Locator is a necessity. Fault Location in Power Cable is designed to locate cable faults, pinpointing the fault location, route tracing, cable identification, voltage withstand make sure cable information management. It could locate all kinds of cable faults for many voltage level cables, including open circuit, short circuit, low insulation, high insulation and flashover faults, etc. Most power cables were buried underground, invisible, and unrealistic, with modern new power cable fault testing equipment, it may discover the fault point quickly, solve problems immediately and restore power source.