Computer hardware information

A printer is a computer peripheral which produces a hard copy of document stored in digital form on paper, plastic, cloths or transparencies. Printers are generally classified by their underlying printing technology. Previously, liquid ink was used in the printing machines. With the advent of new printing technology, many innovative technologies have arrived. One of the latest and most popular technologies is the advanced laser technology. In this kind of printing machine, the Xerographic principle is used. Laser printing machines are available in both colour and monochrome varieties.

In the market, several brands are available and the most popular printer manufacturing companies are HP, Epson, Intex etc. Among them, HP is one of the best selling printers manufacturers - in both inkjet and laser forms.

There are two category of printing machines that are available nowadays. The two primary categories are impact and non-impact printers. The printing machines which are using impact technologies work by touching the paper to fabricate text and images on it. Dot matrix printers come under this category. On the other hand, the non-impact printers do not actually touch the paper, they generally use the blower or bubble technology to take a print out. Both Inkjet and laser printers fall under this category.

Apart from the Inkject and laser printers, there are many types of printing machines that are available in the market. The most common types are Solid Ink printers, Dye-sunlimation printer, Inkless printer, Electrolytic printer, Spark printer, Barcode printer etc. The mostly used printers are Inkjet printer. Inkjet printers that are operated by variably-sized droplet of liquid or molten material (ink). They are the most common type of computer printer for the general consumers due to their high quality of output, capability of printing in vivid colours, ease of use and low cost. The due sublimation printer uses heat to transfer dye to a medium such as a plastic card, paper or canvas. The process is usually to lay one colour at a time using a ribbon that has colour panels.

Now that we have gathered valuable information about the printers, we will be able to make sound decisions when it comes to their usage.

Bit error ratio (BER) measurement is the fundamental measurement of the quality of the fiber optic communication system. It measures the system’s probability that transmitted bits will be correctly received as logic ones and zeros.

Bit error ratio is the ratio of the number of bits received incorrectly compared to the number of bits transmitted in a specified time interval or quantity of bits. The typical acceptable BER levels range from 1e-9 to 1e-12.

Equipment for testing BER

The equipment used to test a fiber optic system’s BER is called BERT (bit error ratio tester). BERT has two fundamental parts: a signal pattern generator and an error detector.

What is a signal pattern generator and how does it work?

The pattern generator is responsible for producing a known data sequence to the system under test. The test patterns are often designed to intentionally stress some aspect of the system under test such as a pattern sequence that is difficult for the clock recovery system to synchronize.

Signal patterns being generated

The patterns being generated also must be similar to the real traffic that will be used in the system. The most common pattern is the pseudo-random binary sequence (PRBS).

PRBS patterns can produce all possible combinations of ones and zeros for a given pattern length. For example, a 2^7-1 PRBS pattern will produce all possible combinations of 7 bit binary numbers.

Pattern generators can generate very long pattern sequence such as a 2^31-1 sequence which has all combinations of 31 bit binary numbers.

What is a error detector and how does it work?

The error detector is on the receiving end of the system being tested. Its functionality is to determine whether the received data matches the transmitted pattern.

The system under test is being fed with the data pattern from the pattern generator. The system has a decision circuit to determine whether the received bit is a one or a zero. The system’s decision circuit output is then fed to the error detector.

The error detector has a built-in internal pattern generator which generates reference pattern identical to the pattern from the pattern generator.

The error detector’s internal reference pattern signal is then synchronized to the output from the system under test. The the bits are compared bit by bit between these two signals. Then the bit error ratio is determined by dividing the number of incorrectly received bits to the total number of bits transmitted.

The relationship between signal power level and bit error ratio (BER)

Another very import system characteristic is called power penalty. What it measures is the relationship between the attenuation between the transmitter and receiver and the bit error ratio. Simply put, the higher the attenuation the worse the bit error ratio. This is often being illustrated on a chart which is a line with negative slope.

In a typical BER characterization of a high-speed system, as the received power is decreased, the signal-to-noise ratio is reduced and the probability of a bit being received in error increases.

NTP servers (Network Time Protocol) are devices that can synchronise a computer network to an authoritative UTC time source. UTC (Coordinated Universal Time) is a global time scale used throughout the world and provided by atomic clocks.

NTP servers can receive UTC time either across the Internet from places such as nist.gov or windows.time. However, it must be noted that Internet based timing references can’t be authenticated and may leave a network vulnerable to malicious attacks such as DDoS (Distributed Denial of Service - normally caused by malware that floods a server with traffic) that blocks access.

Fortunately dedicated NTP servers can receive an authenticated timing reference through either the GPS network (Global Positioning system) or specialist long wave radio broadcasts normally emitted from a national physics laboratory. Some NTP servers can receive both signals and even use them at the same time to ensure better accuracy.

GPS NTP servers are extremely easy to install as most time server manufacturers supply easy-to-use software with their devices.

Normally a GPS NTP server consists of a rack mount NTP time server, A GPS receiver and IEC Power Cables.
For installation first locate a suitable area for the rack mount NTP Time Server in the rack mount enclosure, bearing in mind you will need to run a cable from this location preferably to the roof of the building or by a window if you are using GPS.

Locate an area to mount the GPS antenna, the ideal place would be the roof of the building with a 180 degree view of the sky but bear in mind that you will need to keep the GPS antenna close to the power source on the roof of the building. Things to avoid are air conditioning units and power distribution units as these will cause electrical interference.

The cable should be run from the rackmount enclosure to the selected mounting position leaving some slack cable in case you need to move the unit at a later date! Note: The maximum workable cable length for a GPS time server is 1000 meters (1km).

The four core cable is attached to the rear of the rackmount NTP Time Server using a small junction box. The standard wiring for the GPS antenna is as follows:

1 - Brown, 2 - Orange, 3 - Yellow, 4 - Green, 5 - Blue, 6 - White

With both units wired first power the GPS antenna then power up the rackmount server. Some time servers gave a small LCD screen at the front where on screen diagnostics are displayed. In most cases the unit will synchronise within 15 minutes, the delay is due to the GPS antenna locating and synchronising to satellites.

The configuration of the NTP Time Server can be achieved over the network using an internet browser.