Correct understanding and use of density meter

The success of a printing house often depends on its speed and flexibility. Due to different products and different service targets, the number of prints is getting less and less, and the variety of jobs is increasing. The medium format printing machine relies on the advantages of cost and price, not only to be able to set quickly, but also to obtain stable production conditions. Automated printing preparation and easy-to-control paper transfer are the main features of medium-format printers.

Medium format printing presses refer to printing presses with a paper width of 66-75 cm. It is mainly 74 in Europe and 66, 72, 75 in Japan. Here is a summary of the information on the medium format printing presses at the recent drupa 2004 exhibition.

Heidelberg (Heidelberg) 74 series

The 74 series has SM CD 74, SM74, and PM74, which are high-end and mid-range medium format models.

Speedmagter CD 74 can use a wide range of thicknesses of paper, cardboard and plastic substrates, durable, can run at the highest speed for a long time, suitable for companies that require multiple shifts to produce industrial packaging and printing all the year round. The digital Prinect CP2000 printer control center supports the operation of quickly changing the paper format and printing materials.

Speedmaster CD 74 has two formats: C format 53 cm X74 cm and F format 60. 5 cm X 74 cm, can be equipped with paper turning device. The models of this series are very flexible. Features include:

· According to the change of paper format and printing materials, the presetting of the paper conveyor is automatically performed, which shortens the time for printing preparation.
· The inking unit can respond quickly because of the Color Fast Solution software.
· Alcolor continuous film forming dampening device can achieve stable water-ink balance.
· AirTransfer paper transfer device with patented Venturi technology can ensure the optimal paper transfer between printing units.
· The developed cleaning device fully meets the requirements of environmental protection.
· The Heidelberg InkLine direct inking system can automatically fill the ink fountain and monitor the ink volume of the ink fountain.
· Prinect Auto Register can carry out fully automatic on-board registration control, reducing the printing time.
· It can remotely control the axial, circumferential and lateral registration of the glazing unit, saving time and reducing waste products at startup.
· DryStar drying system with infrared, hot air and cold air modules can adjust the paper feeding to the best.
· The pre-setting of the delivery mechanism can ensure that the delivery is neat. The paper brake function can adjust the brake parts remotely.
· Fully automatic adjustable paper ancestor turning device.

At present, there are many types and models of density meters manufactured abroad. Generally speaking, the first English letter of the density meter model indicates the first letter of the English word of the nature and characteristics of the density meter. For example: T stands for transmission and R stands for reflection. (M) stands for density meter, O stands for dot area tester, TR stands for transmission and reflection, OT stands for dot area transmission density meter, TD stands for transmission density meter, and RD stands for reflection density meter. The Arabic number behind the model of the density meter is the serial number of the density meter.

The domestic model has two supplements: CMF, which stands for color reflection density meter, and CMT, which stands for transmission density meter.

1. Measurement of reflection densitometer

A calibrated densitometer must be used to measure the reflection density. All reflection density values ​​and dot expansion / TVI in SNAP are based on equipment in the ISO T state, and they comply with ANSI / ISO 5/3 and 5/4 standards. When printing on newsprint or other rough paper, SNAP recommends a hole diameter of 4mm.

In all cases, the size of the aperture should be determined in conjunction with the measurement. All measuring instruments are non-polarized. The density profile is absolute, including paper density. The calculation of dot gain / TVI value should be in accordance with ANSI / CGATS.4 (based on Murray-Davies equation). Overprint rate measurement should also comply with ANSI / CGATS.4 (based on Preucil Overprint Equation).

2. Measurement of transmission densitometer

Although the transmission densitometer measurement is to display the light and positive color panchromatic light values, the transmission densitometer measurement is based on the latter. The UGRA ladder ruler is used for the correction of the percentage dot area. In this ladder ruler, the 0.5% light-colored area is used as the zero reference color scale (film base fog). The recommended aperture size is 3mm. In any case, the size of the aperture should be determined in combination with the actual measurement. The test must conform to CGATS.9

Composition of standard density meter

The density meter has 3 basic components (of course there are proofs to be measured). These 3 components include:

1. Lighting system

It is composed of lamps, lighting optical path and power supply for lamps to emit light. The light emitted by the lamp is converted to conform to the ANSI / ISO standard to provide light with a certain color quality (for example, to balance red, green, and blue light), called light source A. This color quality is very close to the quality of the light emitted from the unfiltered tungsten filament lamp. It can be powered by a consistent circuit) However, regardless of the light and power source, the luminaire and power source must be guaranteed to be known as the part of the incident light in this ratio.

2. System for collecting light and measuring

This system consists of a light receiver, an optical path to collect light, and a dichroic filter that transmits only part of the visible spectrum to the light receiver and blocks other parts of the light. This light collection system usually includes color filters to match the sensitivity of the entire spectrum to some of the mentioned standards. The color filter sets previously used by the density meters used in printing and publishing are approximately equivalent to the color separation characteristics in the printing process. These spectral values ​​have been redefined by the ANSI IT2 committee to produce a written standard called the T state. This engineering specification can match the density meters produced by the same manufacturer, as well as the density meters produced by different density meter manufacturers. The density specification of state T is the result of design, measurement and calibration according to the standard response definition.

3. Signal processing system

The signal processing system obtains electronic signals representing incident light and received light energy, and performs calculation and display. This system may be a simple ratio detector, connected to the logarithmic calculation circuit of an analog or digital display, and may also include storage functions to handle functions derived from dot gain and contrast.

Is it necessary to exclude paper density when measuring with a densitometer? Setting paper to zero now does not mean that the user does not have to subtract the density of the paper from the reading. We want to subtract the density of the paper from the density of the solid ground and the density of the screen tone. For the purpose of better communication, this convention must be followed. Another meaningful attribute of printed matter minus paper density is the density of quarter tones. The density of the quarter tones minus the paper density (the relative density of the quarter tones area) can better explain the effect of the printing ink, or the hue itself, because most of the density obtained from the side measurement comes from the paper. However, if the profile is absolute and the paper density is included, solid ink density measurements and important printing attributes (such as print contrast, color cast, and gray balance) are better linked to the human eye's perception of the printed image. All in all, if the purpose of using a density meter is to provide objective measurements that have a good connection with what the press operator actually sees, the measurement should be absolute, including the density of the paper. It is also very useful to measure and monitor the quality of unprinted paper (such as relative color and brightness) with a modern density meter using three color filters. After being equipped with a densitometer and mastering the standardized data of the printing process, We can carry out comprehensive and data-based quality control of the plate-making process and printing process.

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