19
9900 Transmitter
RELAY HIGH and LOW Settings
Depending on the desired function of the circuit attached to the Open Collector (R1) output, it may be necessary to have the
Open Collector turned “on” or “off” when the criteria for the activation of this output are met.
If the 9900 is set to operate in RELAY LOW mode, when the user-de
fi
ned condition for the activation is met (e.g. exceeding an
alarm limit) the Open Collector switch is turned “on.” If wired as standard “NPN-style” output (see previous page) the logic level of
the attached control system or PLC input consequently becomes “low” logic level (when NORMAL is set to OPEN).
If a high input logic level is required for activation, it can be accomplished in one of three ways.
In order of preference,
1. Change the Open Collector (Relay 1) output function to “high” in the instrument's RELAY menu, or
2. Wire the Open Collector (R1) output “PNP” style as described on the previous page, or
3. Set the Open Collector (R1) to NORMAL CLOSED in the RELAY menu.
Fail-Safe Behavior
No matter the setting, the Open Collector output turns off if the 9900 loses power. This must be taken into account when evaluating
system failure consequences. If the system layout requires a “closed” or “on” condition for the output in case of power loss, a
mechanical dry-contact relay (NC contacts) must be used instead of the Open Collector (R1) output.
Voltage and Current Limitation
The supply voltage in the Open Collector output circuit MUST be limited to the speci
fi
ed maximum Open Collector voltage
(see operating manual for speci
fi
c instrument). The use of a quality 5 to 24 V (depending on the application) regulated power supply
(not supplied) is recommended.
The current through the Open Collector switch also must be limited. Typical Open Collector outputs allow only for 10 to 50 mA
switch current. Exceeding this current limit can burn out the Open Collector output components immediately.
Load and Pull-Up/Down Resistor Considerations
By utilizing basic arithmetic and Ohm’s Law, the safe limits of load resistance can be determined. When the Open Collector switch is
closed, almost the entire supply voltage is applied to the load (e.g., the pull-up or pull-down resistor, the alarm horn input, a potential
power relay coil or annunciator lamp).The resulting current through the load and through the Open Collector switch, as well, can be
calculated as:
(Current)
=
(Supply Voltage)
/
(Load Resistance)
Example: Set a relay R1 to turn
on at a low setpoint of 5.5 gpm
with a time delay of 15 seconds
and turn off at 8.0 gpm.
Remember,
SET LOW + hysteresis = OFF point:
5.5 + 2.5 = 8.0
System Start-up: Step 3
Set your relay functions to your own application requirements.
Next step: System Setup (see page 25).
1. Go to the Relay Menu (RELAY
fl
ashing on screen, press ENTER).
2. If prompted, select desired source.
3. Press
▼
to relay
MODE
selection screen.
4. If necessary, press
►
and then
▼
or
▲
to select
R1 MODE LOW
.
Press ENTER to confirm.
5. Press
▼
to
R1 SET LOW
. Press
►
to enter GPM value of 5.5.
6. Press ENTER to save.
7. Scroll
▼
to the
R1 HYSTERESIS
menu.
8. Press
►
to edit.
9. Set the hysteresis for this relay. This affects the turn off only:
2.5 gpm
.
10. Press ENTER.
11. Scroll down
▼
to the
R1 ON DELAY
menu.
12. Press
►
to edit.
13. Set the turn-on delay in seconds for the relay:
15.0
.
14. Press ENTER.
15. Exit to View Mode.
●
Relay function can be tested in the RELAY menu.
Once a setting is saved it becomes immediately active.
Relay Functions
Relay and Open Collector Outputs
