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Variation on the SCAN function (special SCAN function)
The multiplexer offers in addition a second SCAN function. With this special SCAN function (command 149,
function 2) an additional parameter is used, which defines the minimum length of the expected number of
data bytes. This can be different for each current loop, but must be set for each current loop that is to be
scanned.
The SCAN function itself takes place as above, however, the response of the transmitter is compared with
the expected data length. If the length of the response is less than the set minimum data length, the answer
is rejected. If the minimum length is 0, the answer is always saved.
Delay on channel change/Loop switch delay (software function when used with RPI)
If the HART multiplexer is used with the RPI HART control module KSD2-HC, a pause time must be inserted
when the multiplexer channel is changed. This pause time is necessary, since the RPI HART control module
has to monitor the communication channel of the multiplexer and recognise the channel change. This pause
time can be set by means of command 161.
All the functions at a glance
The following list gives all the functions once again at a glance:
•
16 channels, extendable to 256 channels by the connection of up to 15 KFD0-HMS-16 slaves.
•
Up to 7936 loops per interface
•
Automatic search of all existing HART field devices (REBUILD)
•
Facility for self-standing cyclic interrogation of the HART variables (SCAN)
•
Acts as a primary or secondary master
•
Fast RS 485 interface (multidrop) with up to 38400 baud
•
Integrated Modem
•
Removable terminals
•
Supply via power rail
•
Approval for zone 2
2.1.7
Start-up sequence
Following connection of the power supply, the device executes an initialisation procedure with self test. The
function is indicated by a flashing green LED, any errors detected are indicated by a red LED. Next a search
is made of the multiplexers in the multiplexer table (command 157) for available HART compatible field
devices (REBUILD). This function is indicated by a flashing orange LED. The REBUILD function can also
be started via the service station, e. g. in order to include connected transmitters in the communication
process during the operating phase. The duration of this function is dependent on the number of connected
transmitters, multiplexer slaves and message repeats in the case of errors, or if an interrogation has not
been answered. The factory setting for the number of repeats is "2". The search duration for this lies
between approx. 30 s and several minutes (full structure).
In addition, transient data are set to their pre-setting. Non-volatile stored data are retained. see section
2.1.10.
2.1.8
Operation
The multiplexer master KFD2-HMM-16 also functions as a HART device (see also section 2.1.10). How-
ever, due to the incorporation into the operating software of the service station (see section 2.3.3), this
remains concealed from the user. The HART commands that are supported by the multiplexer can be found
in section 6.1.
For HART communication with the transmitters, the commands of the service station are passed through
without modifications.
Subject to reasonable modifications due to technical advances.
Pepperl+Fuchs Group • Tel.: Germany (06 21) 7 76-0 • USA (330) 4 25 35 55 • Singapore 7 79 90 91 • Internet http://www.pepperl-fuchs.com
HART Multiplexer Master KFD2-HMM-16
Copyright Pepperl+Fuchs, Printed in Germany
Product description
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