PD2-6060
Helios Large Display Dual-Input Meter Instruction Manual
15
Modbus RTU Serial Communications
Serial communications connection can be made to the onboard RS485 terminal block or USB connector
shown in Figure 7. If RS232 is required, an RS485 to RS232 adapter (PDA7485) may be used. See
Ordering Information on page 5 for additional information.
Relay Connections
Relay connections are made to two six-
terminal connectors labeled RELAY1 –
RELAY4 on Figure 7. 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 12. 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 13. 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 14. 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: PDX6901.
Note: Relays are de-rated to 1/14th HP (50 watts) with an inductive load.
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.
4
3
6
5
2
1
RELAY4
RELAY3
4
3
6
5
2
1
RELAY2
RELAY1
C
R
C
R
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