ProtEX-MAX PD8-6100 Strain Gauge, Load Cell, and mV Meter
Instruction Manual
28
Switching Inductive Loads
The use of snubbers to suppress electrical noise is
strongly recommended when switching inductive
loads to prevent disrupting the microprocessor’s
operation. The snubbers 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 16. 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.
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.
Figure 17. Low Voltage DC Loads Protection
RC Networks
(Snubbers)
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:
Note:
Relays are de-rated to 1/14th HP (50 watts) with an
inductive load.
RS-485 Connections
The RS-485 connections are made to a five terminal
connector used for Modbus RTU serial
communications. The RS-485 terminals include
Transmit Data (DO) and (/DO), Receive Data (DI) and
(/DI), and Signal Ground. See
information.
There are three diagnostic LEDs: Transmit Data (TX),
Receive Data (RX) and METER LINK to show when
the meter is transmitting and receiving data from other
devices.
Figure 18. RS-485 Diagnostic LEDs
RS-485 Multi-Drop Connection
When using more than one meter in a multi-drop
mode, each meter must be provided with its own
unique address. The meter address (Slave ID) can be
programmed between 1 and 247. The transmit delay
can be set between 0 and 199 ms. The parity can be
set to even, odd, or none with 1 or 2 stop bits.
To change the meter address:
1. Press and hold the Menu button for three
seconds to access Advanced Features menu of
the meter.
2. Press Up arrow until Serial (
SEriaL
) menu is
displayed and press Enter,
Addres
is displayed.
3. Press Enter to change meter address using Right
and Up arrow buttons. Press Enter to accept.
4. Press Menu button to exit and return to Run
Mode.
Three-Wire Connection
In order to wire the five pins for use as a three-wire
half-duplex RS-485 connection, it is necessary to
create a jumper connection between DI to DO and /DI
to /DO- as shown below.
C
R
C
R
__ __
DI
DI DO DO
Summary of Contents for ProtEX-MAX PD8-6100
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