DPM-500 Analog Input Meter Instruction Manual
13
Modbus RTU Serial Communications
Serial communications connection is made to an RJ45 connector labeled M-LINK on Figure 6. For
interfacing to the DPM-500, 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, digital I/O).
Relay Connections
Relay connections are made to two six-terminal connectors labeled RELAY1
– RELAY4 on Figure 6.
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 11. 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 12. 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 13. Low Voltage DC Loads Protection
RC Networks Available from BinMaster
RC networks are available from BinMaster and should be applied to each relay contact switching an inductive load.
Part number: PDX6901.
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
Use a diode with a reverse
breakdown voltage two to
three times the circuit voltage
and forward current at least as
large as the load current.
