In the context of industrial process control, a ‘transmitter’ converts sensor measured units into an electrical signal then directs this data via cabling or wirelessly.
When speaking in the context of industrial process control, a ‘transmitter’ is a device that converts sensor measured units into an electrical signal then directs this data (via cabling or wirelessly) to be received by a display or instrumentation control device within the system. This central control hub is not necessarily located nearby or in some cases not necessarily even in the same premises.
A transmitting unit is usually defined by the sort of sensor data it is converting and sending. Examples of this are temperature transmitters, pressure transmitters or airflow transmitters. They will then further be described by any additional features such as being din-rail mounting compatible, resistance to corrosive chemicals, analogue, digital or USB programmable.
Industrial transmitters have additional physical requirement as they are often subject to relatively harsh conditions. Operating temperature conditions can vary and fluctuate excessively. This combined with vibrations and industrial chemicals make the need for robust units a must.
Analog transmitters are the most commonly used type in most industrial sectors. The transmitter is connected to the rest of the system via 2 wires which create something know as the ‘current loop.’ The two wires can be used for both powering the unit and for transmitting signals typically at a range of 4 mA to 20 mA, It must be noted that when a system is transmitting low level analogue signals over wires, noise and electrical interference will cause some degradation of the signal.
Smart transmitters use the same two-wire setup as analogue transmitters but utilize a microprocessor to digitize the data from the sensor. This allows for built in compensation for sensor nonlinearity (making the output more accurate) as well as allowing for multiple sensors to be connected to the transmitter. While the final output to control systems is still in analogue format the overall data quality and integrity is higher with the use of smart micro processing units.
Intelligent transmitters were developed due to increased use of digital data in industrial control systems. A new standard in industrial communication interfacing known as fieldbuses provided the advantages of digital data transmissions, higher measurement certainty, remote unit adjustments and identification and a new networking capability. An intelligent transmitter is a transmitter that that is capable of both digital signal processing and digital two-way communication as well as utilizing an accepted industrial protocol. The biggest concern for instrumentation specialists is which protocol or standard the unit utilizes and overall compatibility with the system. The most common protocols used today would be Foundation fieldbus, HART anf ProfiBus.
This intelligent technology allows operators to measure multiple parameters using a single transmitter and to tailor built in diagnostic requirements.
In an increasing number of industrial situations wireless sensors are an appropriate upgrade to classic industrial transmitters. This is because current generation sensors offer flexible system solutions which are ideal for temporary installations and in processes with moving parts/objects. Such wireless sensor networks can be comprised of hundreds or thousands of intelligent sensors. This allows for complex network mapping that can provide advanced solutions to today’s processing environments.