Helios PD2-6080/PD2-6081 Modbus
®
Scanners
Instruction Manual
21
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 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 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 21. 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:
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 22. 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 23. Analog Output Supply Powering Other
Devices
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
+
-
