HART MODEM ELECTRICAL DRAWING

Each of the 4-20 mA current loop is supplied with a 24 VDC power line, which is a very common voltage in the electrical cabinets operating in the European industry.
( Actually, it could be any other low voltage direct current, according to the country and the current usages. )
Each of the current loop is composed of :
- One 4-20 mA PLC analogical input.
- One HART analogical sensor and its transmitter ( including a current converter ).
  ( « Q » = Flow sensor ; « L » = Level sensor ).
- One 250 ohms load resistor dedicated to each modem connection.
The load resistors can stay wired permanently, with or without any modem being connected. This avoids opening the current line before using a modem.
The interface must be parallel connected to the load resistor, so it can be permanently installed if necessary ( when a remote connection is needed for instance ).
The matter being analogical measuring, it is highly advised to use a stable and isolated power supply, apart the power supplying digital IO and other « common » devices. A switched mode power supply ( SMPS ) is a pertinent choice.
Whether the analogical inputs are completely galvanic isolated, they can be inserted serially anywhere in their respective loop.
For the NON isolated analogical inputs or/and which have inputs containing a common link, they can not be inserted anywhere in the loop.