User guide

Multi Process Meter Instruction Manual
22
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 13. 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 meter's relay screw terminals. An RC network
may also be installed across the load. Experiment for best results.
Figure 14. Low Voltage DC Loads Protection
RC Networks Available from Dwyer Instruments, Inc.
RC networks are available from Dwyer Instruments, Inc. and should be applied to
each relay contact switching an inductive load. Part number: PMA-13.
Note: Relays are de-rated to 1/14th HP (50 watts) with an inductive load.
C
R
C
R
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.