Precision Digital PD6000 - Manual (Page 21)

Model PD6000 Analog Input Process Meter Instruction Manual
21
Switching Inductive Loads
The use of suppressors (snubbers) is strongly recommended when switching
inductive loads to prevent disrupting the microprocessor’s operation. The sup-
pressors 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 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 con-
firm proper operation.
3. Install the RC network at the meter'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 1/14th HP (50 watts) with an inductive load.
Use a diode with a reverse
breakdown voltage two to
three times the circuit vol-
tage and forward current at
least as large as the load
current.