PD8-6262 Explosion-Proof Dual Analog Input Flow Rate/Totalizer
Instruction Manual
28
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 20. Relay Connections
Interlock Relay Feature
As the name implies, the interlock relay feature
reassigns one, or more, alarm/control relays for use
as interlock relay(s). Interlock contact(s) are wired to
digital input(s) and activate the interlock relay. This
feature is enabled by configuring the relay, and the
corresponding digital input(s), see
Interlock Relay (Force On) Feature
on page
In the example below, an Interlock Contact switch is
connected to a digital input, which will be used to
force on (energize) the Interlock Relay. The Interlock
Relay and the Control Relay are connected in series
with the load.
•
When the Interlock Contact is closed (safe), the
Interlock Relay energizes, allowing power to flow
to the Control Relay; the corresponding front
panel LED is on.
•
When the Interlock Contact is open, the
corresponding front panel LED flashes (locked
out), the Interlock Relay is de-energized,
preventing power from flowing to the Control
Relay and the load.
Figure 21. Interlock 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 22. 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 totalizer's relay screw
terminals. An RC network may also be installed across
the load. Experiment for best results.
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.
Figure 23. 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
