Manual ELW 170 / ELW 180
May 2020
page 5
7.1 Operating mode auto restart
The relays have the following function:
REL1 (contacts 5, 6, 7): Alarm function without interlock
REL2 (contacts 8, 9, 10): Flow monitoring
Once the operating voltage has been applied and the desired flow speed has built up after the start delay
(constants see technical data ), relay 2 energises (contacts 8/9 close) and the downstream unit is released.
This therefore prevents harmful heating / humidification without air removal. If the necessary air speed isn't
reached after the start delay, relay 1 switches to alarm contact 6/7. A drop in flow below the set value during
operation occurs once the switch-off delay has passed.
Contacts 8/9 are opened (heating off) and contacts 6/7 are closed at the same time (alarm). Both relays are
not interlocked in this state. When the flow is detected again, the measuring cycle starts automatically with-
out the device having to be disconnected from the power supply (stand-by mode).
7.2 Function of the setting potentiometers
Four potentiometers can be used to influence the device’s switching behaviour. They are located on the
right-hand side of the PCB and have the functions described below, working from top to bottom.
7.2.1 “Switch-on delay” speed controller
Allows the switch-on delay to be set to between 15 and 120 seconds.
Factory setting 15 seconds.
7.2.2 “Switch-off delay” speed controller
Allows the switch-off delay to be set to between 2 and 20 seconds.
Factory setting 2 seconds.
7.2.3 “Hysteresis” speed controller
Allows the hysteresis to be set to between 1 and 10% of the measuring range. Hysteresis prevents the output
from being switched repeatedly if the measurement moves around the set switching point.
Factory setting 1%.
7.2.4 “Flow speed” speed controller
This speed controller is used to set the flow speed (0,2...10m/s). Should the speed fall below the flow speed,
a switching process is triggered. The “Flow” LED can be used to judge whether the current flow value is above
or below the set switching value.
Factory setting 1.5 m/s.
LED off = flow < set value
LED on = flow > set value
7.3 Display elements
Three LEDs are provided as display elements. Their functions are explained below.
7.3.1. “Relay 1” and “Relay 2” LEDs
These two LEDs indicate the switching state of the two associated relays.
LED on = relay energised
LED off = relay deactivated
The circuit diagram provided on the housing shows the relay when deactivated.
7.3.2. “Flow” LED
Used to set the flow speed and check function. During normal operation, this LED goes out as soon as the
flow speed falls below the set value. The LED’s behaviour depends on the set flow speed and hysteresis,
not however on the switch-on and switch-off delay, which only influence the switching state of the relays.
Flashing of the LEDs indicates that there is a faulty connection between the sensor and control unit.
