Precision Digital PD6310 - Manual (Page 29)

Model PD6210 & PD6310 Batch Controllers Instruction Manual
29
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:
C
R
C
R
Figure 19: 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 controller's relay screw terminals. An
RC network may also be installed across the load. Experiment for
best results.
Figure 20: 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 1/14th HP (50 watts) with an inductive load.
Use a diode with a reverse
breakdown voltage two to
three times the circuit volt-
age and forward current at
least as large as the load
current.