A PC Smaller Than a Credit Card

The CM-X270 is a small Computer on-Module board designed to serve as a building block in embedded applications. The CM-X270W has all the components required to run operating systems such as Linux and Windows CE. Ready packages for these operating systems are available from CompuLab.

The small size and low power consumption of the CM-X270 allows its integration into hand-held and mobile applications, while its low price makes it an ideal selection for cost-sensitive applications. Based on Intel's XScale architecture, the CM-X270 delivers a price/performance ratio significantly better than that of any other platform.

The feature set of the CM-X270 module combines a 32-bit CPU, SDRAM, Flash Disk and vital computing peripherals. For embedded applications, the CM-X270 provides a 32-bit PCI bus, 100Mbit Ethernet, serial ports, general purpose I/O lines and many other essential functions. An on-board 2700G Multimedia Accelerator enhances the feature set with support of XGA display resolution and MPEG-2 / MPEG-4 decoders.

An integrated WLAN (WiFi) interface implements 802.11b industry standard wireless connectivity. The CM-X270 is the first and only CoM in the market implementing this essential feature.

The standardized CAMI ("CompuLab's Aggregated Module Interface") connectors of the CM-X270 module allow interchangeability with other Computer-On-Module's available from CompuLab, enabling the flexibility required in a dynamic market where application requirements can change rapidly.

Transformer Oil

The functions of the transformer oil are

i. to provide dielectric strength.

ii. to protect the insulation system, and

iii. cooling.

Transformer Oil

Transformer oil is a mineral insulating oil derived from crude petroleum. It is a mixture of various hydrocarbons.

Aliphatic compounds

(open chain compounds) with the general formula Cn H2n+2 and Cn H2n.

Many oils also contain certain aromatic compounds (closed chain or ring compounds) related to benzene, naphthalene and derivatives of these with aliphatic chains.

Good transformer oil must

• insulate
• prevent flash over of the exposed parts within the equipment and
• it must effectively transform the heat from the core to the radiating surface.

Transformer Oil – Characteristics

The characteristics of new transformer oil is given in I S 335 / 1983.

Characteristics	Requirement
Appearance	Clear and Transparent, Free from suspended particles
Density at 27 0 C (Max.)	0.89 g / cc
Dielectric Strength (BDV) - New - After Filtration	30 kV (rms) 50 kV (rms)
Dielectric Dissipation Factor (Tan d) At 90 0 C – ( Max.)	0.005
Neutralization Value Total Acidity (Max.) b. Inorganic acidity / alkalinity	0.03 mg. KOH / gm. Nil

Characteristics	Requirement
Kinematic Viscosity at 27 0 C (Max.)	27 cSt.
Interfacial Tension at 27 0 C (Max.)	0.04 N / m
Flash Point	140 0 C
Pour Point	-9 0 C
Corrosive Sulphur	Nil
Oxidation Stability Neutralization Value after oxidation (Max.) Total Sludge after oxidation (Max.)	0.40 mg. KOH / gm. 0.10 percent by weight
Specific resistance (Resistivity) At 90 0 C ( Min.) At 27 0 C (Min.)	30 x 10 12 ohm-cm. 500 x 10 12 ohm-cm.

TRANSFORMER OIL - QUALITY CHECKING

There is no single test to judge the quality of transformer oil. Each test is significant within its limits and is able to give only general information about the overall condition of the oil.

The most popular test is the dielectric strength test. If the dielectric strength is low, the oil is unfit for use regardless of any other condition. Good transformer oil must have 60 kV withstand voltage between two brass electrodes - 12.7 to 13 mm dia, arranged horizontally with their common axis not less than 40 mm above the bottom of the cell, with a gap of 2.5 mm.

TRANSFORMERS IN GENERAL USE

1. Star - Star YyO or Yy6
2. Delta - Delta DdO or Dd6
3. Star - Delta Yd
Delta - Star Dy
4. Star - Zigzag Yz
5. Delta - Zigzag Dz

Star-Star (Yy0 or Yy6)

Most economical connection in HV power system to interconnect two delta system and to provide neutral for grounding both of them.
Tertiary winding stabilises the neutral conditions.

In star connected transformers, load can be connected between line and neutral, only if

(a) the source side transformers is delta connected or

(b) the source side is star connected with neutral connected back to the source neutral.

Delta - Delta (Dd 0 or Dd 6)

This is an economical connection for large low voltage transformers.

Large unbalance of load can be met without difficulty.

Third harmonics are damped out as the windings are closed mesh.

But the absence of a star point is dis-advantageous in some cases.

Delta - Star (Dy or Yd)

Common for distribution transformers.

Star point facilitates mixed loading of three phase and single phase consumer connections.

The delta winding carry third harmonics and stabilises star point potential.

Delta-Star connections is used for step-up generating stations.

If HV winding is star connected there will be saving in cost of insulation.

But delta connected HV winding is common in distribution network, for feeding motors and lighting loads from LV side.

Star-Zig-zag or Delta-Zig-zag (Yz or Dz)

These connections are employed where delta connections are weak. Interconnection of phases in zigzag winding effects a reduction of third harmonic voltages and at the same time permits unbalanced loading.

This connection may be used with either delta connected or star connected winding either for step-up or step-down transformers. In either case, the zigzag winding produces the same angular displacement as a delta winding, and at the same time provides a neutral for earthing purposes.

The amount of copper required from a zigzag winding in 15% more than a corresponding star or delta winding. This is extensively used for earthing transformer.

Ladder logic

Ladder logic is the main programming method used for PLCs. As mentioned before, ladder logic has been developed to mimic relay logic. The decision to use the relay logic diagrams was a strategic one. By selecting ladder logic as the main programming method, the amount of retraining needed for engineers and trades people was greatly reduced.

Modern control systems still include relays, but these are rarely used for logic. A relay is a simple device that uses a magnetic field to control a switch, as pictured in Figure 2.1. When a voltage is applied to the input coil, the resulting current creates a magnetic field. The magnetic field pulls a metal switch (or reed) towards it and the contacts touch, closing the switch. The contact that closes when the coil is energized is called normally open. The normally closed contacts touch when the input coil is not energized. Relays are normally drawn in schematic form using a circle to represent the input coil. The output contacts are shown with two parallel lines. Normally open contacts are shown as two lines, and will be open (non-conducting) when the input is not energized. Normally closed contacts are shown with two lines with a diagonal line through them. When the input coil is not energized the normally closed contacts will be closed (conducting).


Relays are used to let one power source close a switch for another (often high current) power source, while keeping them isolated. An example of a relay in a simple control application is shown in Figure 2.2. In this system the first relay on the left is used as normally closed, and will allow current to flow until a voltage is applied to the input A. The second relay is normally open and will not allow current to flow until a voltage is applied to the input B. If current is flowing through the first two relays then current will flow through the coil in the third relay, and close the switch for output C. This circuit would normally be drawn in the ladder logic form. This can be read logically as C will be on if A is off and B is on.

The example in Figure 2.2 does not show the entire control system, but only the logic. When we consider a PLC there are inputs, outputs, and the logic. Figure 2.3 shows a more complete representation of the PLC. Here there are two inputs from push buttons.

We can imagine the inputs as activating 24V DC relay coils in the PLC. This in turn drives an output relay that switches 115V AC, which will turn on a light. Note, in actual PLCs inputs are never relays, but outputs are often relays. The ladder logic in the PLC is actually a computer program that the user can enter and change. Notice that both of the input push buttons are normally open, but the ladder logic inside the PLC has one normally open contact, and one normally closed contact. Do not think that the ladder logic in the PLC needs to match the inputs or outputs. Many beginners will get caught trying to make the ladder logic match the input types.

Many relays also have multiple outputs (throws) and this allows an output relay to also be an input simultaneously. The circuit shown in Figure 2.4 is an example of this, it is called a seal in circuit. In this circuit the current can flow through either branch of the circuit, through the contacts labeled A or B. The input

B will only be on when the output B is on. If B is off, and A is energized, then B will turn on. If B turns on then the input B will turn on and keep output B on even if input A goes off. After B is turned on the output B will not turn off.


See also:
PROGRAMMABLE LOGIC CONTROL
PLC Programming
PLC Connections
Ladder Logic Inputs and Outputs

Phase-change Random Access Memory (PRAM)

The Phase-change Random Access Memory (PRAM) is more scalable than any other memory architecture being researched and features the fast processing speed of RAM for its operating functions combined with the non-volatile features of flash memory for storage.


A key advantage in PRAM is its extremely fast performance. Because PRAM can rewrite data without having to first erase data previously accumulated, it is effectively 30-times faster than conventional flash memory. Incredibly durable, PRAM is also expected to have at least 10-times the life span of flash memory.


PRAM will be a highly competitive choice over NOR flash, available beginning sometime in 2008. Samsung designed the cell size of its PRAM to be only half the size of NOR flash. Moreover, it requires 20 percent fewer process steps to produce than those used in the manufacturing of NOR flash memory.

Samsung’s new PRAM was developed by adopting the use of vertical diodes with the three–dimensional transistor structure that it now uses to produce DRAM. The new PRAM has the smallest 0.0467um 2 cell size of any working memory that is free of inter-cell noise, allowing virtually unlimited scalability.


The Korean company announced that it has completed the first working prototype of what is expected to be the main memory device to replace high density NOR flash within the next decade. Adoption of PRAM is expected to be especially popular in the future designs of multi-function handsets and for other mobile applications, where faster speeds translate into immediately noticeable boosts in performance. High-density versions will be produced first, starting with 512 Mb.


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