Types of Thermocouples

Thermocouples can be manufactured from a diversity of metals covering a temperature range of 200 ^oC to 2,600 ^oC. Various combinations of metals i.e. calibrations exist for thermocouples. There are approximately thirteen types of standard thermocouples available in the industry and out of them eight have been designated with an internationally known letters. The eight designated thermocouple types are listed below:

1. Type K – This type of thermocouple is made up of Chromel-Alumel. It belongs to the chromium-nickel aluminum group and has a fairly linear e.m.f./temperature curve.
2. Type J – This type of thermocouple having limited temperature range is made up of Iron-Constantan.
3. Type E – It is made up of Chromel-Constantan and offers great sensitivity. It is primarily used in cryogenic i.e. low temperature range. Being a non magnetic type, it proves to be advantageous in variety of applications.
4. Type N – It is made up of Nicros-Nisil and offers excellent thermoelectric stability. It is extremely resistant to high temperature oxidation.
5. Type T – This type of thermocouple is made up of Copper-Constantan. It is found extremely useful in food, environmental and refrigeration applications.
6. Type S – It is made up of Platinum rhodium
7. Type R – It also contains Platinum rhodium and somewhat identical to type S
8. Type B - It is an extremely stable thermocouple made up of Platinum rhodium only. Its output is found to be very small at room temperature and offers less sensitivity in the lower range.

The above thermocouple types can be categorized into two groups i.e. Base metal and Rate or Noble metal. Type K, J, E, N and T fall into the Base metal category whereas Type R, S and B come into the Noble metal category.
In general, there are four classes of thermocouples which are mentioned below:

1. Home body class which is also referred to as Base metal Type. The temperature range for these types of thermocouples varies from -200°C to 1200°C.
2. Upper crust class, also known as Rare metal or Precious metal or Noble metal Type. The temperature range for these types of thermocouples varies from 0°C to 1600°C.
3. Rarified class, also known as Refractory metal Type
4. Exotic class which consists of various tungsten alloy thermocouples and many other standard and developmental devices. It is typically designated by Type W.

Each thermocouple type or calibration has a specific range of temperature and environment. However, the maximum temperature possible depends upon the thermocouple wire diameter. The most preferred types of thermocouples are found to be K and N types since they perform well at high temperatures, whereas another industry preferred thermocouple is T type as it offers high sensitivity, low cost and simple operation.

Protocol Gateways

Force & its Effects

Force & its Effects Definition 

A quantity competent enough to modify the size, shape, or motion of an object is termed as force. In other words “A force is an influence (such as a push, gravity, or friction) that causes an object either to change its velocity or to store energy through deformation”. Since force is a vector quantity, it has got both direction and magnitude. In case, a body is in motion, the energy of its motion can be quantified as the momentum of the object i.e. the product of its mass and its velocity. When the body is free to move, its velocity will be changed by the action of a force.

Units of Measurement

The precise measurement of force is significant in many areas, like engine thrust determination, the weighing of large structures, and materials testing. The magnitude of a force is measured in:

1. Newtons (In the SI system): One Newton is defined as the force required to accelerate a mass of one kilogram at a rate of one metre per second, per second
2. Pounds (In the British/American system)

Basic Forces

Four basic forces found in nature are:

1. Gravitational Force: It is the force of attraction between any two bodies in the universe. It is the weakest of all and also the easiest to observe. It is always attractive and has an infinite range.
2. Magnetic Force: It can be the force between two magnets or force on a magnet placed in a magnetic field. It can be either attractive or repulsive.
3. Strong nuclear Force: It is a strong force with a short range. It is a non-central force which acts within the nucleus. It is not directed along the line joining the centres of the interacting particles.
4. Weak nuclear Force: Its range is shorter than the strong nuclear force and this type of force is considerable only for certain nuclear processes like radioactive beta decay.

Pressure

It is the ratio between force acting on a surface and the area of that surface. It is measured in units of force divided by area:

1. Pounds per square inch (psi)
2. Newtons per square meter, or Pascals

Whenever an object is subjected to an external stress i.e. pressure with the aim to cause a reduction in its volume, this process is called compression. The majority of liquids and solids are practically incompressible, whereas gases are not.

Boyle's Law

It is the first Gas Law which states that the pressure and volume of a gas are inversely proportional to one another i.e. PV = k, where P is pressure, V is volume and k is a constant of proportionality.

Charles' Law

It is the Second Gas Law which states that the volume of an enclosed gas is directly proportional to its temperature i.e. V = kT, where T is its absolute temperature.

Third Gas Law

According to this law, the pressure of a gas is directly proportional to its absolute temperature i.e. P = kT. After combining the three relationships we get the ideal gas law i.e. PV = kT. This approximate relationship holds accurate for many gases at relatively low pressures and high temperatures.

Analog to Digital Converter

An analog-to-digital converter (commonly abbreviated as ADC, A/D or A to D) is a device which converts continuous signals to discrete digital numbers. In general, an ADC is an electronic device basically employed for transforming an input analog voltage or current in to a digital number proportional to the magnitude of the voltage or current.
An analog signal is continuous in time and it is required to convert this to a flow of digital values. For that reason it is essential to define the rate at which new digital values are sampled from the analog signal. The rate of new values is called the sampling rate or sampling frequency of the converter.

Analog to Digital Converter - Continued

RSLinx Diagnostic Tools

RSLinx includes a wealth of diagnostic information to assist us in analyzing our system. Whether it's trouble-shooting a communication problem or analyzing network throughput, RSLinx provides the needed information. Diagnostics fall into following three major categories:

1. Networks: Diagnostic counters track server information such as messages sent, messages received, messages acknowledged, communication errors, and timeouts. Performance counters give throughput in terms of packets/second.
2. Station: Diagnostic counters indicate information for a selected station such as messages sent and received, message retries, and packet errors.
3. OPC/DDE: Multiple dialogs for DDE clients, OPC Groups, Optimized Packets, and OPC/ DDE server connections display diagnostic information specific to the category. A Communication event log displays information specific to an OPC/DDE transaction. 

Data Collection Modes

RSLinx

RSLinx Classic is an inclusive communication server which provides plant-floor device connectivity for a wide variety of Rockwell Software applications such as

• RSLogix 5/500/5000
• RSView32
• FactoryTalk View Site Edition
• FactoryTalk Transaction Manager

Besides, numerous open interfaces are provided for third-party HMI, data collection and analysis packages, and custom client-application software. RSLinx Classic is capable enough to support multiple software applications at the same time, communicating to a range of devices on many different networks.
RSLinx Classic 2.x is now associated to RSLinx Enterprise, a new product that provides supreme connectivity to Logix processors. RSLinx Enterprise provides data services for distributed FactoryTalk View Site Edition products, FactoryTalk Transaction Manager, FactoryTalk Historian, and FactoryTalk Metrics applications.
One can communicate from anywhere to anywhere using RSLinx Classic. RSLinx is available in multiple packages to meet the demand for a variety of cost and functionality requirements.

RSLinx Benefits

No Parity

Parity checking is also used in communication between modems. Here, parity checking can be selected to be even (a successful transmission will form an even number) or odd. Users may also select no parity, meaning that the modems will not transmit or check a parity bit. When no parity is selected (or defaulted), it's assumed that there are other forms of checking that will detect any errors in transmission. No parity also usually means that the parity bit can be used for data, speeding up transmission. In modem-to-modem communication, the type of parity is coordinated by the sending and receiving modems before the transmission takes place. Specifically, the Peripheral Component Interconnect bus and the I/O bus controller use the odd parity method of error checking.

Parity Limitations

Parity Checking

It is also known as Vertical Redundancy Check (VRC). It is a method of adding a parity bit to a data stream to check that data for any errors. It is an elementary method of detecting simple, single-bit errors in a memory system. It requires the use of parity memory, which provides an extra bit for every byte stored. This extra bit is used to store information to allow error detection. Parity checking on newer systems normally requires the appropriate BIOS setting to be enabled. ECC-only modules cannot be used in straight parity-checking mode.

Modbus to BACnet Protocol Converters