P
RO
V
U
™ PD6363 Dual Analog Input Rate/Totalizer
Instruction Manual
18
Modbus RTU Serial
Communications
Serial communications connection is made to an
RJ45 connector labeled M-LINK. For interfacing to the
P
RO
V
U
®
, use the PDA1232 for RS-232 or the
PDA1485 for RS-485. The same port is used for
interfacing with all expansion modules (
e.g.
external
relays, additional 4-20 mA outputs, digital I/O).
Relay Connections
Relay connections are made to two six-terminal
connectors labeled RELAY1
– RELAY4. Each relay’s
C terminal is common only to the normally open (NO)
and normally closed (NC) contacts of the
corresponding relay. The relays’ C terminals should
not be confused with the COM (common) terminal of
the INPUT SIGNAL connector.
Figure 19. Relay Connections
Switching Inductive Loads
The use of suppressors (snubbers) is strongly
recommended when switching inductive loads to
prevent disrupting the microprocessor’s operation.
The suppressors also prolong the life of the relay
contacts. Suppression can be obtained with resistor-
capacitor (RC) networks assembled by the user or
purchased as complete assemblies. Refer to the
following circuits for RC network assembly and
installation:
Figure 20. AC and DC Loads Protection
Choose R and C as follows:
R: 0.5 to 1
Ω for each volt across the contacts
C: 0.5 to 1 µF for each amp through closed contacts
Notes:
1. Use capacitors rated for 250 VAC.
2. RC networks may affect load release time of
solenoid loads. Check to confirm proper
operation.
3. Install the RC network at the meter's relay screw
terminals. An RC network may also be installed
across the load. Experiment for best results.
Figure 21. Low Voltage DC Loads Protection
RC Networks Available from
Precision Digital
RC networks are available from Precision Digital and
should be applied to each relay contact switching an
inductive load. Part number:
Note: Relays are de-rated to 1/14th HP (50 watts)
with an inductive load.
C
NO
NO
NC
NC
C
RELAY4
RELAY3
4
3
6
5
2
1
C
NO
NO
NC
NC
C
RELAY2
RELAY1
4
3
6
5
2
1
C
R
C
R
