More complex, more compact, more efficient — this is the credo for system engineers in the chemical and process industries. Of course, this also increases the MCR effort required to squeeze production into tighter and tighter process schedules. Phoenix Contact’s new pluggable test disconnect terminals now simplify servicing and maintenance.
In the chemical and process industries, many new approaches designed to make production quicker, cheaper, and more flexible have been tested in the last few years — and quite successfully so. This has allowed the industry to recover relatively quickly after the 2009 crisis. The success was due not only to container solutions and modularization, but also to retrofitting and system expansion.
These tendencies have also facilitated the increased use of Hart (Highway Addressable Remote Transducer) protocol-capable sensors and control valves. This technology uses the classic 4-20 mA current loop as a transmission medium for a modulated data transmission signal in accordance with the Bell 202 FSK standard, in which communication is conducted by means of signal sequences of varying frequencies alternating between command and response on simple twisted-pair cables. This keeps down implementation costs, and the actual analog measurement signal remains unaffected.
In this way, multiple variables or pieces of information can be transmitted, and remote diagnosis or device configuration can be carried out.
What Are Disconnect Terminals For?
Hart is used with a number of sensors for measuring temperatures, pressures, vacuums, filling levels, distances, conductivities, densities, and pH values. Valves, servo-motors, inputs and outputs of all kinds, and analog values are also controlled using Hart. This can be done in three ways:
- readjustment and calibration of measurement values,
- troubleshooting in complex systems,
- parameterization or querying of device configurations using a computer.
It is often necessary to connect measuring or diagnostic devices to a current loop — for test measurements of the parameters received by the sensors on the one hand, and for evaluation of the switching states or system parameters on the other.
In conventional control systems, i.e., where no current loop is used for data communication, a short signal interruption does not necessarily cause any problems. But if the current loop is also the transmission medium, interruption causes communication with the Hart modem to be broken off and a system error message to be sent. That is why interruption-free connection is indispensable for Hart-controlled systems.
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