P
RO
V
U
™ PD6088/PD6089 Modbus
®
Scanner
Instruction Manual
17
Relay Connections
Relay connections are made to two six-terminal
connectors labeled RELAY1
– RELAY4 on the back
of the scanner. 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 15. Relay Connections
Switching Inductive Loads
The use of snubbers to suppress electrical noise is
strongly recommended when switching inductive
loads to prevent disrupting the
microprocessor’s
operation. The snubbers 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 16. 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 scanner'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 17. Low Voltage DC Loads Protection
RC Networks (Snubbers) 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 1/14 HP (50 watts) with
an inductive load.
4-20 mA Output Connections
Connections for the 4-20 mA transmitter output are
made to the connector terminals labeled mA OUT.
The 4-20 mA output may be powered internally or
from an external power supply.
Figure 18. 4-20 mA Output Connections
Analog Output Power Supply
The internal 24 VDC power supply powering the
analog output may be used to power other devices, if
the analog output is not used. The I+ terminal is the
+24 V and the R terminal is the return.
Figure 19. Analog Output Supply Powering Other
Devices
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
4-20 mA Input
Remote Display, PLC,
Chart Recorder, Etc.
-
+
R
I-
I+
1
3
2
RELAY1
mA OUT
24 V
12-35 VDC
Power
Supply
+
4-20 mA
Input Meter
-
+
R
I-
I+
1
3
2
RELAY1
3
2
1
-
24 V
mA OUT
Internal Power Supply
and Analog Output
3
2
1
Active Output Loop
Passive Output Loop
R
I-
I+
1
3
2
24 VDC
Powered
Device
24 V
+
-