Information On The Correct Operation Of Reed Contacts In Bühler Level Switches; Adjusting The Level Contacts - Bühler technologies Nivotemp NT 64 Guía Rápida

Nivotemp NT 64, Nivovent NV 74
For direct installation to the tank, insert the switching tube
into the designated bore (per DIN 24557, Part 2) with rubber-
ised cork seal on the tank. It secures to the flange using the in-
cluded screws and seals. Please be sure the float can move
freely and to leave enough space between the tank wall and
add-ons.
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.
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
BX100020 ◦ 12/2017
9
cycles. This is reduces
B
Contact
Load
RC circuit
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!
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.

4.3 Adjusting the level contacts

cm scale on the back
Cordless bistable level contacts
Function: falling NO contact (NC)
or falling NC contact (NO
Spacing grid 10 mm
Change the NC/NO contact function by
turning the contacts 180°
Thermal element TK / PT / KT
The contacts required for the float are mounted to a galvanic-
ally gold-plated with cm scale with plastic screws. The contact
housings have different colours and may only be mounted to
the contact strip in the following order.
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
Contact strip
Bühler Technologies GmbH 7