Electrical Connections; Information On The Correct Operation Of Reed Contacts In Bühler Level Switches - Bühler technologies Nivotemp NT MD Guía Rápida

Nivotemp NT MD
After removing the float, where applicable, be sure the mag-
net inside the float is above the fluid level. This can easily be
verified with a piece of iron to determine the magnet position
inside the float.
DANGER
Electric voltage
Risk of electric shock
When connecting devices, please note the maximum voltages
and currents currents (see technical data) and use the correct
wire cross-sections and circuit breakers.
When selecting the connection lines, also note the maximum
operating temperatures of the devices.
Installation in special areas of application:
If the device will be installed outdoors or in wet areas, the
maximum operating voltage is max. 16 V DC effective or 35 V
DC.
The flange-mounted display units can be swivelled vertically
by approx. 270° so they are easier to read. Please note the
built-in swivel stop. You will notice more resistance when
reaching the stop. Turning it beyond this stop may damage
the display unit.

4.2 Electrical connections

Electricity is supplied via plug connectors. Please refer to the
appendix for installation dimensions, nominal voltage and
plug configuration.
The temperature switching outputs are PNP transistors (see il-
lustration):
Supply voltage
Note: When measuring the switching output with high-load
measuring device inputs or when used as a frequency output,
the load must be set to 10 kΩ between the output and earth
(GND) to avoid faulty measurements.
4.3 Information on the correct operation of reed
contacts in Bühler level switches
Based on their construction, reed contacts are very long last-
ing and reliable components. Yet the following should be con-
sidered when using them:
Life of reed switches
The life of reed switches can be up to 10
by high stress and / or incorrect or the absence of protective
circuits when switching inductive, capacitive or lamp loads.
It's therefore important to ensure NEVER to exceed one or sev-
eral of the maximum approved limits, even temporarily, and
to install a contact protective circuit for loads which are not
purely ohmic. Using test lamps when installing the devices is
BX100022 ◦ 11/2020
also prohibited, as these can temporarily allow too much cur-
rent to flow, which can damage the reed contacts. In this case
non-volatile testing equipment should always be used.
Contact protective circuits for reed switches
For direct current voltage a recovery diode per figure A must
be connected parallel to the contact.
For alternating current voltage an RC circuit per Figure B and
Table 1 must be connected parallel to the contact.
Please note the max. voltage/load ratings of the respective
level contacts!
Voltages and currents
All Bühler level contacts with reed switch can switch minimal
Switching voltages of 10 µV and minimal switching currents
of 1 µA.
The maximum values specified for the respective contact
types apply.
Level contact with reed switches can therefore be used for SPS
applications as well as for high loads (within the maximum
limits) without hesitation.
Contact material
All reed switches in Bühler level contacts use rhodium as the
contact material for the actual contact areas.
Magnetic fields
Avoid external magnetic fields, including from electric mo-
tors. These can interfere with the function of the reed
switches.
Mechanical loads
Do not expose the level switch to strong blows or bending.
5 Operation and control
9
cycles. This is reduces
A
Contact
Load
Recovery diode
Load in VA 10
Voltage at R/Ohm C/µF R/Ohm C/µF R/Ohm C/µF
contact V
24 22 0.022
60 120 0.0047
110 470 0.001
230 470 0.001
NOTICE
The device must not be operated beyond its specifications.
B
Contact
Load
RC circuit
25 50
1 0.1 1 0.47
22 0.022 1 0.1
120 0.0047 22 0.022
470 0.001 120 0.0047
Bühler Technologies GmbH 9