Glossary
Fail-safe signal modules
Installation and Operating Manual, 01/2010, A5E00085586-10
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M switch
Each fail-safe digital output of SM 326 DO 8 x DC 24V/2A PM consists of one DOx P switch
(current source) and one DOx M switch (current sinking). The load is connected between the
P and M switches. The two switches are always active in order to power the load.
Measuring location identification tag
Unique identifier for the measuring point, consisting of 8 characters. It is saved in the
→ HART field device and can be modified and read out via → HART commands.
Modem
A modem (MOdulator / DEModulator) is a device that converts binary digital signals to
→ frequency shift keying signals and vice versa. A modem does not encode any data, but
converts the physical form of the signals.
Module fault
Module faults may be caused by external faults (for example, missing load voltage) or by
internal faults (for example, processor failure). Internal faults always require module
replacement.
Module redundancy
A module and a second identical module are operated in redundant mode in order to
enhance availability.
Monitoring time
→ PROFIsafe monitoring time
Monodrop
In a monodrop communication system, a maximum of two devices are connected to the
same transmission line, e.g., channel of the HART analog module and a → HART field
device. The → HART protocol and the analog signal can be used simultaneously in this
method.
The HART short address of the field device is 0.
MTA
Marshalled Termination Assemblies
Multidrop
Up to 15 field devices can be connected to a HART master in a multidrop communication
system. Communication is exclusively via the → HART protocol, the analog signal cannot be
used in this method.
The HART short address of the field device is between 1 and 15.
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