ProtEX-MAX PD8-765 Explosion-Proof Process & Temperature Meter
Instruction Manual
32
Figure 15. Two-Wire RTD Input Connections
Lead wire compensation for two-wire RTDs can be
applied using the
Adjust
menu.
Figure 16. Four-Wire RTD Input Connections
The four-wire RTD connection is similar to the
three-wire. One of the leads of a four-wire RTD is not
connected and may be clipped off.
The three-wire connection provides sufficient lead
wire compensation to provide accurate readings even
with long leads.
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:
Note: Relays are de-rated to 1/14th HP (50 watts) with an
inductive load.
Relays and 24 V Output
Connections
Relay connections are made to a six-terminal
connector labeled RELAY1, RELAY2. See
. The COM (common) terminals
of the relays should not be confused with the COM
(common) terminal of the SIGNAL connector. The
24 VDC output (available on AC powered units only)
is available at the connector labeled 24V OUT, next to
the relays connector.
Figure 17. Relay & 24 V Output Connections
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 18. AC and DC Loads Protection
Choose R and C as follows:
R: 0.5 to 1
for each volt across the contacts
C: 0.5 to 1 µF for each amp through closed contacts
Notes:
1.
Inductive relay rating is 1/14 HP (50 W) at 115/230 VAC
2.
Use capacitors rated for 250 VAC.
3.
RC networks may affect load release time of solenoid loads.
Check to confirm proper operation.
4.
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 19. Low Voltage DC Loads Protection
24V OUT
P+
P-
COM
NO
NO
NC
NC COM
REL AY2
REL AY1
4
3
6
5
2
1
2
1
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.
