Information On The Correct Operation Of Reed Contacts In Bühler Level Switches; Adjusting Level Contacts (Nt61, Nv71 Only); Electrical Voltage - Bühler technologies Nivotemp NT 61 Guía Rápida

Nivotemp NT 61, NT 61-HT, NT 63, NT 63-
LTD/Nivovent NV 71, NV 73
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.
4.2 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
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.
A
Contact
Load
Recovery diode
Load in VA 10
Voltage at R/Ohm C/µF
contact V
24 22 0.022
60 120 0.0047
110 470 0.001
230 470 0.001
Please note the max. voltage/load ratings of the respective
level contacts!
6 Bühler Technologies GmbH
9
cycles. This is reduces
B
Contact
Load
RC circuit
25 50
R/Ohm C/µF R/Ohm C/µF
1 0.1 1 0.47
22 0.022 1 0.1
120 0.0047 22 0.022
470 0.001 120 0.0047
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.

4.3 Adjusting level contacts (NT61, NV71 only)

The level measurement contacts are mounted on a perforated
rail inside the protective tube. These are arranged per order
specifications but can be moved if necessary.
Depending on the model, the perforated rail will also have
electronic assemblies. These are positioned so they do not
limit the setting range of the level contacts. Please be sure not
to damage the assemblies during installation or removal.
Models with the designation K, KN or LTD supply a continuous
4-20 mA signal. These devices do not require configuration.
For devices with 230 V mains voltage:
DANGER

Electrical voltage

Electrocution hazard.
a) Disconnect the device from power supply.
b) Make sure that the equipment cannot be reconnected to
mains unintentionally.
c) The device must be opened by trained staff only.
d) Regard correct mains voltage.
• Disconnect the voltage supply.
• Disconnect the plug.
• Models NT61: Unscrew the plug base. For plug-in connect-
ors with screw-in plug base, unscrew the top hexagon
ring and pull the complete pin insert up until the bottom
of the base can be unscrewed freely.
• Models NV71: Remove filter cover and element. Unscrew
and remove the filter case. Unscrew the flange cover from
the level switch.
• Carefully pull the perforated rail with contacts out the
top.
BX100019 ◦ 08/2020