Precision Digital PD570 - Manual (Page 38)

If the load inductance is over the controller specifications, the output may need a RC filter (snubber) or
diode to properly handle frequent relay switching operations.
7.10 Use of an External Relay
!
CAUTION
External AC
Power
External DC
power
(1) DC External Relay
(2) AC External Relay
CR Filter (snubber)
(Connect directly to the relay coil terminals)
Controller
R
!
CAUTION
!
CAUTION
R
Relay
(Verify relay coil ratings are less than the voltage and current ratings of the relay
contacts of the controller)
Diode
(Connect directly to the relay coil terminals)
Controller
!
CAUTION
!
CAUTION
Relay
(Verify relay coil ratings are less than the voltage and current ratings of the relay
contacts of the controller)
Switching Inductive Loads
When using switching in ductive loads, the use of RC networks (snubbers) for AC loads or diodes for DC loads is
recommended 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 or diodes assembled by the
user or purchased as complete assemblies.
For AC loads, choose R and C as follows:
R: 0.5 to 1
Ω for each volt across the contact
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. RC networks are available from Precision Digital and should be applied to each relay contact switching an
inductive load. Part number: PDX6901.
PD570 Series Nova Process and Temperature Limit Controller Instruction Manual
38