Pulsafeeder Pulsar DLCM - Manual (Page 129)

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15. MODBUS Mode
15.1 Introduction
The serial communications supplied with the DLC/M is similar in operation to that with the 4-20mA
signal. The [MODE] key controls the current operating mode: MANUAL, ANALOG (4-20mA) or
MODBUS. Serial communications can occur with the DLC/M regardless of the mode setting. Never the
less, only when the DLC/M is in the MODBUS MODE can a value be written – changing the operation of
the device. In any other mode, values can only be read. Note that even in MODBUS MODE, the arrow
keys cannot be used to adjust the flow, stroke or speed.
15.2 General Discussion
A PC or PLC MASTER controls a DLC SLAVE by writing to the Holding Registers for Percent Stroke,
Percent Speed and Motor Status values. When the MASTER READS from the Stroke and Speed, it
retrieves the User Desired Position and User Desired Speed. When the MASTER WRITES to the Stroke
and Speed, it changes the Digital-Stroke and Digital-Speed values. This allows the application of the
RATIO and REVERSE ACTING factors and checking of the end points limits. The written values must
be in the range of 0.00% – 100.00% (0-10000). In addition, if this is NOT a DLCM, writing anything at
all to the Motor Speed will return an error. The FLOW RATE cannot be set directly by the MASTER, it
is calculated from the Stroke and Speed settings.
W ARNING : F OR SAFETY , IF AN OPERATOR WANTS TO DISABLE THE MODBUS R EMOTE
C
ONTROL OF THE
DLCM,
THEN THEY MUST SWITCH THE
DLCM
OUT OF
MODBUS MODE.
T URNING OFF THE MOTOR WILL NOT PROTECT THEM AGAINST THE PUMP BEING TURNED BACK
ON BY THE
PC/PLC. W
HENEVER PERFORMING MAINTENANCE
,
THE POWER SHOULD BE
REMOVED COMPLETELY FROM THE DLCM.
To prevent operators from modifying the operation of the DLC (e.g., changing the MODE from
MODBUS to MANUAL), Tamper Proof Security should be invoked. When doing this, carefully select
options in the {MODBUS SIG. FAIL} menu. If the DLC/DLCM is configured to restore to MANUAL
MODE, and a MODBUS signal failure is detected, the PC/PLC will no longer be in control of the DLC.
If Security is enabled, then operators will not be able to control the DLC/DLCM either (except for the
motor key, which is never protected by security).