Tuesday 31 July 2012

Types of Thermostats


Electromechanical or Manual thermostats: These are old-fashioned mercury units which consist of internal coils to expand or contract in response to temperature change. These types of thermostats are getting obsolete because of following two reasons:
  1. Digital thermostats are able to more accurately register and respond to temperature changes
  2. Purchase of products containing mercury has been restricted or banned in many states
In spite of above mentioned reasons manual thermostats remain popular owing to their low cost, the familiarity of their controls' design and ease of their use.

Manual digital thermostats: They make use of an electronic temperature sensor to register changes in the room temperature. These changes are then compared with the settings selected by the user. If there is a difference between the room temperature and the set temperature, a command is sent to the heating or cooling system necessitating action. For manual digital thermostats we need to physically adjust the setting of our preferences whenever we would like to adjust the room temperature. New digital thermostats have no moving parts to measure temperature and instead rely on thermistors or other semiconductor devices like a resistance thermometer or resistance temperature detector. They use either a relay or a triac to act as switch to control the HVAC unit. Units with relays will operate millivolt systems, but often make an audible "click" noise when switching on or off.

Programmable digital thermostats: These are up gradation of the digital manual thermostats and also referred to as setback thermostats or clock thermostats. They are more convenient to use and can help save energy costs. Once we program the thermostat to fit our lifestyle and schedule, the thermostat works automatically year-round. We simply need to program the temperatures into the memory of the unit, along with the times of day that we would like the changes to occur. Based on the model, a thermostat can be programmed in following three ways:
  1. 5 - 2 programming: Maintains a set schedule for five days (weekdays), and then switches to an alternate schedule for the other two days (weekends).
  2. 5 - 1 - 1 programming: Maintains a five day schedule (weekdays), then switches to first individual day (Saturday), then second individual day (Sunday).
  3. 7 day programming: Allows the maximum flexibility for those with frequently-changing schedules by allowing us to program each day individually.
Other Advanced Thermostats: Various highly developed models have touch screens and the aptitude to work with home automation or building automation systems. More expensive models have a built-in PID controller, so that the thermostat knows in advance how the system will react to its commands.

Monday 30 July 2012

Thermostat Applications & Location


Thermostats make our life more comfortable. They are used widely in HVACR which means heating, ventilation, air conditioning and refrigeration. Major applications of thermostats include:
  1. Temperature control of a room to the comfort level of the occupants
  2. Temperature control of a refrigerator to ensure that food is kept fresh
  3. Temperature control of the operating theatre and a host of other applications

Location of Thermostat

Following point should be kept in mind while deciding the location of thermostat:
  1. It should be located far-off from the room's cooling or heating vents or device. However, it is exposed to general airflow from the rooms to be regulated.
  2. An open hallway may possibly be most appropriate for a single zone system, where living rooms and bedrooms are operated as a single zone.
  3. If the hallway is closed by doors from the regulated spaces then these should be left open when the system is in use.
  4. If the thermostat is too close to the source controlled then the system will tend to "short cycle", and numerous starts and stops can be irritating and in some cases shorten equipment life. A multiple zoned system can save considerable energy by regulating individual spaces, allowing unused rooms to vary in temperature by turning off the heating and cooling. 

Tuesday 24 July 2012

FieldServer's Main Features


A Fieldserver is also known as a communications bridge, protocol converter, or communications gateway. It is basically a protocol translation device. It is user configured to enable devices which employ different communications protocols to communicate with one another. FieldServers are capable to support multiple protocols in a single bridge. Fieldserver’s are physical devices which work as a gateway enabling different devices employing different protocols to interface with each other. Besides solving communication and protocol conversion problems a Fieldserver improves response times in distributed data acquisition and control systems as well.

Main Features

  • An extensive driver library is available from FieldServer Technologies which gives a broad range of interoperability solutions. Its library of protocols numbers more than 110.
  • The FieldServer acts like an Ethernet gateway and enables new and legacy PLCs, RTUs and SCADA devices to link to Ethernet for plant-wide communications.
  • Based on the model, the FieldServer is equipped with combinations of Serial, Ethernet and LONWORKS ports as well as various fieldbus ports.
  • The internal poll-block caching capability assures that data from Server devices is straight away available to the client devices when required.
  • Data can be cached from slower devices or remote units for immediate access by the client device.
  • The Hot Standby option for the FieldServer is available as and when dual redundancy is required. 

Monday 23 July 2012

BACnet MSTP


BACnet MSTP is a token passing protocol. Here the MS stands for Master - Slave and the TP stands for Token Passing. This flavor of BACnet is mainly used for connecting field devices to controllers / routers / control applications. BACnet MSTP uses RS485/EIA485 as its physical layer which allows up to 128 devices to be installed on a single network with a max physical length of 4000ft and speeds up to 115k baud. Using repeaters allows the length to be increased. General baud rates are 19200, 38400 and 76800. All devices have got to operate at the same baud rate and upon autosensing the baud rate, more and more devices configure themselves correctly.

MSTP master and slave

Only nodes with the token are permitted to initiate service requests like requests for data. A device that receives a request, a request that requires a response, might respond without having the token. Based on this behavior it is simple to understand the difference between a MSTP master and slave. A slave is a device that can only send responses. A master is an initiator of a service request.

Friday 20 July 2012

XML Key Benefits


Separates Data from HTML: To display dynamic data in HTML document, one needs to perform lot of work to edit the HTML each time the data changes while with XML, data can be stored in separate XML files. By a few lines of JavaScript, we can read an external XML file and update the data content of our HTML.


Simplifies Data Sharing: In the real world, computer systems and databases store data in incompatible formats whereas XML data is stored in plain text format. This provides a software- and hardware-independent way of storing data and makes it much easier to create data which different applications can share.


Simplifies Data Transport: By means of XML, data can be conveniently exchanged between incompatible systems. One of the most time-consuming challenges for developers is to exchange data between incompatible systems over the Internet. Exchanging data as XML reduces this intricacy to a great extent, since the data can be read by different incompatible applications.


Simplifies Platform Changes: Upgrading to new platforms (either hardware or software), is always very time consuming since large amount of data needs to be converted and incompatible data is frequently lost. However, XML data is stored in text format which makes it easier to expand or upgrade to new operating systems, new applications, or new browsers, without losing any data.


Makes our Data More Available: Since XML is independent of hardware, software and application, it can make our data more available and useful. Diverse applications can access our data, not only in HTML pages, but also from XML data sources. Via XML, our data can be available to all kinds of reading machines like Handheld computers, voice machines, news feeds, etc, and make it more available for blind people, or people with other disabilities.


Used to Create New Internet Languages: Many new Internet languages are created with XML. Some of the examples are given below:

  • XHTML the latest version of HTML
  • WSDL for describing available web services
  • WAP and WML as markup languages for handheld devices
  • RSS languages for news feeds
  • RDF and OWL for describing resources and ontology
  • SMIL for describing multimedia for the web 

Thursday 19 July 2012

HTTP Request methods


HTTP defines following eight methods for indicating the preferred action to be performed on the identified resource

  1. HEAD: This method asks for the response identical to the one that would correspond to a GET request, but without the response body. This method is useful for retrieving meta-information written in response headers, without transporting the entire content.
  2. GET: This method is used for requesting a representation of the specified resource. GET should not be used for operations that cause side-effects, such as using it for taking actions in web applications.
  3. POST: It submits data to be processed to the identified resource. The data is included in the body of the request. This may result in the creation of a new resource or the updates of existing resources or both.
  4. PUT: Used for uploading a representation of the specified resource.
  5. DELETE: It is used for deleting the specified resource.
  6. TRACE: Use of this method echoes back the received request, so that a client can see what intermediate servers are adding or changing in the request.
  7. OPTIONS: This request method returns the HTTP methods supported by the server for specified URL. This can be used to check the functionality of a web server by requesting '*' instead of a specific resource.
  8. CONNECT: It converts the request connection to a transparent TCP/IP tunnel, generally to facilitate SSL-encrypted communication (HTTPS) through an unencrypted HTTP proxy.
HTTP servers are required to implement at least the GET and HEAD methods and, whenever possible, also the OPTIONS method.

Convert HTTP to other communication protocols

Wednesday 18 July 2012

Modbus Register types


Most commonly used Modbus register types includes:

1. Coil (Discrete Output)
2. Discrete Input
3. Input Register
4. Holding Register

The address range for Modbus was originally defined from 0 to 9999 but now the currently specified range has been updated from 0 to 65,535. This address range is valid for each type of Modbus register. The function code specified in the Modbus query message packet determines what register type is being referenced. Reference range for all the four register types is mentioned below:
  • 0x Coil 00001-09999
  • 1x Discrete Input 10001-19999
  • 3x Input Register 30001-39999
  • 4x Holding Register 40001-49999
Sometimes it becomes necessary to access more than 10,000 of a register type. Additional register types and reference ranges include the following:
  • 0x Coil 000001-065535
  • 1x Discrete Input 100001-165535
  • 3x Input Register 300001-365535
  • 4x Holding Register 400001-465535
It is mandatory to use six digit register references while using the extended register referencing to easily differentiate between holding register 40001 and coil 40001. "If coil 40001 is the target, it must appear as 040001". [1]

Limitations

In spite of its unfussiness and simplicity, Modbus protocol embraces few restrictions as well. The most considerable limitation is its incapability to sustain and uncover description of large binary objects. Moreover Modbus being a Master/slave protocol provides no means for a field device to “Report by exception”. Also Modbus addressing restrictions up to 247 devices per data link confines the range of field devices requiring connection to a master station.

Thursday 12 July 2012

RSNetWorx


RSNetWorx products provide design and configuration management services for following installations:
  1. ControlNet International's ControlNet
  2. Open DeviceNet Vendor Association's DeviceNet networks
  3. Ethernet I/P
With the help of RSNetWorx, maximum productivity can be attained with our ControlNet and DeviceNet installations. This simple software interface makes it possible to define and configure the devices on our network rapidly without any trouble. Devices can be defined either offline using drag and drop operations or online by using RSLinx to browse a ControlNet or DeviceNet network.

Tuesday 10 July 2012

RSLogix Architect


RSLogix Architect is very simple software which can powerfully manage all RSLogix5000 based controller configuration files, network configurations, and produced and consumed tag relationships. It offers tools for:
Via RSLogix Architect, we can create pages which are a living view of our network and controller. These pages are used in our automation system since control hardware layout containing the chassis, controllers, and communication modules is drawn on these pages. We can also draw networks which enable us to connect the controllers together. After the controllers get connected together through networks, produced and consumed tag relationships can be easily configured from one location. RSLogix Architect software is an ideal complement to Integrated Architecture.

Monday 9 July 2012

FactoryTalk ProductionCentre - Benefits II


Returned Merchandise Authorization (RMA) and Repair
Use of FactoryTalk ProductionCentre assists in

  • Enhanced global repair efficiencies by spending time and resources using data, leaving the task of data collection to FactoryTalk ProductionCentre
  • Generating quick response to customer inquiries by providing customers with real-time order status via the web
  • Rapid diagnosis of defects by relying on a view of past repairs, manufacturing history and most common repairs
  • Product quality improvement by enforcing repair processes and incorporating engineering or field change orders into returned merchandise
Supplier Manager

FactoryTalk ProductionCentre works as an excellent supplier manager as it

  • Provides full traceability of supplier components, reducing time required for root-cause analysis and recall management
  • Includes supplier part management and cross-referencing capabilities
  • Produces metrics on supplier quality such as inspection results and supplier quality trends
  • Implements supplier sampling plans including skip lot, ANSI Z1.4, ANSI Z1.9, Dodge Romig, Zero acceptance, and first article inspections
  • Integrates with CAPA to provide Supplier Corrective Action Requests (SCAR)
Analytics

This exclusive software is capable enough to
  • Convert operational data into information for fact-based decision-making
  • Use a single data model to span supplier, manufacturing and repair for unsurpassed insights that disparate systems can easily overlook
  • Provide more than 50 web-based standard reports
  • Real-time response and alerting with live transactional data reporting 

Friday 6 July 2012

FactoryTalk eProcedure Benefits


Procedure automation benefits with no expense of equipment automation are generally offered by FactoryTalk eProcedure. Few of its significant benefits include:
  • It supports 21 CFR Part 11 and other regulatory requirements
  • Streamlines data collection
  • Provides the same consistency as automated controls for manual operations
  • Utilizes an interactive, web-based interface to sequence and document manufacturing operations
  • Allows choice of media for delivering operating instructions through HTML procedure delivery 

Thursday 5 July 2012

Rockwell Automation Software/RSLogix Micro - System Requirements


Following are the requirements that must be fulfilled before using RSLogix Micro Programming software:
  1. IBM-compatible PC with Pentium® processor
  2. Microsoft Windows XP and later
  3. 32 MB of RAM (64 MB recommended)
  4. 50 MB of free hard disk space (or more based on application requirements)
  5. 16-color VGA Graphics Adapter, 640 x 480 or greater resolution (256-color 800 x 600 optimal)
  6. Products require the use of RSLinx Classic Lite. RSLinx Classic Lite is included with RSLogix 500 

Wednesday 4 July 2012

XIF Files


Files which define the network visible interface for one or more LONWORKS devices are known as LONMARK device interface i.e. XIF files.

Device Interface

It is basically an interface to a device which is exposed over a LONWORKS network. It only exposes the inputs to the algorithms and the outputs from the algorithms and does not expose the internal algorithms of a device. A device interface contains following information:
  1. Device’s self documentation information
  2. Number of address table entries
  3. Number of message tags
  4. Number, types, and directions of network variables.
The device interface can be inquired over the network to a great extent with the help of a network tool. The device manufacturer establishes the completeness of a queried interface. For instance, a device manufacturer may opt to embed network variable names in a device to make certain that the queried network interface includes these names.

Benefits

Following are the benefits to using device interface files:
  1. A device interface file may contain information that is not available in a device such as network variable names.
  2. Besides, a device interface file can be employed during network engineering when the device is not accessible from the network engineering tool. 

Tuesday 3 July 2012

Subnetting


Subnet 

It is used to break the network into smaller more efficient subnets to avoid excessive rates of Ethernet packet collision in a large network. Such subnets can be arranged hierarchically, with the organization's network address space partitioned into a tree-like structure. Routers are employed to manage traffic and constitute borders between subnets.

A typical subnet is a physical network served by one router. For example, an Ethernet network consisting of one or several Ethernet segments or local area networks, interconnected by network switches and network bridges or a Virtual Local Area Network. It is possible to divide a physical network into several subnets by configuring different host computers to use different routers. While improving network performance, subnetting increases routing complexity, as each locally connected subnet is typically represented by one row in the routing tables in each connected router.

Subnet mask

It enables us to identify that part of an IP address which is reserved for the network, and the part which is available for host use.

Monday 2 July 2012

Routers - Introduction


Router is a networking device whose software and hardware are typically customized to the tasks of routing and forwarding information. For instance, on the Internet, information is directed to various paths by routers. Routers connect two or more logical subnets, which do not essentially map one-to-one to the physical interfaces of the router. It operates in two different planes:

  1. Control plane: It is a plane in which the router learns the outgoing interface that is most appropriate for forwarding specific packets to specific destinations.
  2. Forwarding plane: A plane which is responsible for the actual process of sending a packet received on a logical interface to an outbound logical interface.

Brief Description

In packet-switched networks like Internet, a router is a device or, in some cases, software in a computer which decides the next packet forwarding point in a network. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any gateway i.e. a point where one network meets another including each point-of-presence on the Internet. A router is often included as part of a network switch.

A router creates and maintains a table of the accessible routes and their conditions and makes use of this information along with distance and cost algorithms to establish the best route for a given packet. Normally, a packet travels through a number of network points with routers before arriving at its final destination. Routing is a function associated with the Network layer i.e. layer 3 in the Open Systems Interconnection (OSI) model (the standard model of network programming). A layer-3 switch is a switch that can perform routing functions.

Router Components