ProtEX PD8-6080/PD8-6081 Explosion-Proof Modbus
®
Scanner Instruction Manual
20
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 11. 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.
Figure 12. 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 1/14 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 13. 4-20 mA Output Connections
Analog Output Transmitter 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.
C
R
C
R
12-35 VDC
Power
Supply
+
4-20 mA
Input Meter
-
+
R
I-
I+
1
3
2
RELAY1
3
2
1
24 V
-
4-20 mA Input
Remote Display,
Chart Recorder, Etc.
-
+
R
I-
I+
MA OUT
1
3
2
RELAY1
3
2
1
24 V
MA OUT
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.
