Overview electro-mechanical, inductive and pneumatic limit signal indicators for pressure gauges
type 1100.1110

are summarized in this overview and their mode of operation and application is described.
Further details you will find in the type sheets 1100.1111 - 1100.1113.

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This limit signal indicators
are used for the closing and opening of electric or pneumatic circuits in dependency
of the pointer position of the pressure measurement device.

With an abatable key the set point indicator is adjusted to the value on which the
switching operation shall take place. The construction of the limit signal transmitter is
made in a way to be able to continue operation above the target value after making
contact. The set point indicators can be adjusted over the whole scale range.

Limit signal indicators have 1 or 2 contacts (special versions up to max. 4 contacts).
Pressure measuring devices with housing-Ø (NG) 100, 160 and 250 or square cases 96 x 96 und 144 x 144 are suited for the installation of limit value switches.

Limit signal indicators are installed below the scale by default (HZ-version).
At NG 250 they are installed on the scale (TZ-version).
The electrical connection is made either with a connection cable through the back of
the housing or by a cable box mounted at the housing. With pneumatic limit value switches the connection is made via a low pressure switch, that is mounted on the back side of the housing.

A distinction is made between the following contact types:
1. Electron-mechanical contacts
(see type sheet 1100.1111)
1.1 low-action contact( S )
1.2 magnetic contact   ( M )
2. Inductive-contact
(see type sheet 1100.1112)( I )
3. Pneumatic-contact
(see type sheet 1100.1113)( P )

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Mode of operation and application
On limit signal indicators with low-action contacts the switching operation is made exactly when the instrument pointer and the set point indicator are above each other.
The contact pins are touching or are seperated. These contacts are not suitabel for high contact loads at normal operation conditions. The mounting must be vibration-free,
because otherwise accidental switching could take place.

If the switching shall take place exactly at the adjusted limit value and the pressure measuring device is not mounted vibration-free our contact protection relays with time delay
are recommended.

Where an aggressive atmosphere may take place, that causes an oxidation of the contacts, at very high switching frequencies as well as in potentially explosive areas our
limit switches with inductive contacts are recommended.

On twice or multiple contacts the set point can be adjusted such, that the switching difference is approximately only 1 % of the scale end value.

On liquid-filled pressure measuring devices low-action contacts are inapplicable. We recommend inductive respectively electric limit signal indicators.

Technical Data

Voltage:max. 250 V
Contact rating:10 W/18 VA
Contact material:silver-nickel 10 µm, gold-plated
Ambient temperature:       
-20°C to + 70°C respectively according to the particular
characteristics of the pressure measuring device.

The contacts are non-inductive.

1.2 Magnetic contacts ( M )
Mode of operation and application
On limit signal indicators with magnetic contacts a screwable permanent magnet is mounted on the carrier arm below the limit value pointer, secured with locking solution. Thereby the contact arm is pulled at the closing contact shortly before reaching the limit value pointer, respectively at isolating contacts the contact seperation is delayed. This switching difference can be 2-5% of the scale end
value according to the straightening force of the discriminating element and the adjusted magnet force. The limit value pointers must be put forward respectively backward by this difference. Because the magnet is screwable, the switching difference
is changeable. The permanent magnet increases the contact pressure (thereby higher contact rating) and protects the contacts against burning through
Limit signal indicators with magnetic contacts are applicable nearly everywhere,
because they are as far as possible immune against vibrations. Their application area can be extended by our contact protection relays.

Where an aggressive atmosphere is expected, that causes an oxidation of the contacts, at very high switching frequencies as well as in potentially explosive area our limit switches with inductive contacts are recommended.
On liquid-filled pressure measuring devices we recommend likewise inductive or electric limit signal indicators.

Technical Data ( M )

Voltage:up to max. 250 V
Contact rating:

up to max. 30 W / 50 VA, the switching current must not excess 1 A, constant current 0,6 A

Contact material:silver-nickel, 10 µm gold-plated.
Ambient temperature:     -20°C to +70°C respectively according the particular measurement device characteristics

Magnetic contact
The contacts are non-inductive.


Mode of operation (load current principle) and application
Inductive limit signal indicators are electric path transducers (proximity switches) without contact according to EN 60947-5-2. Essentially the system consists of a transistor oscillator, whose voice coils are arranged to both sides of the slot initiators. When a metall flag dips into this air gap the high frequency oscillation is damped. Only a little control current (≤ 1mA) is flowing, the initiator gets highly-resistive, the relay in the downstream isolating
amplifier drops out. When the flag is leaving the initiator, a high control current ( ≥ 3 mA) is flowing again. The initiator gets low-resistive, the relay in the downstream isolating amplifier picks up. The path transducer is mounted on a carrier arm that
is joined with the set point indicator, while the control flag is moved by the actual value pointer. The switching operation takes place exactly when the control flag is in the middle of the path transducer. The velocity, with which the control flag is moved, does not matter here. Inductive limit signal indicators are wear-resistant due to the lack of mechanical contact and thereby absolute maintenance-free and also corrosion-resistant, because all electrical parts are cast watertight in a plastic housing with resin.

The torque that appear on the actual value pointer by the control flag is as low as on low-action contacts. For class 0,6 pressure measuring devices reactionless inductive limit signal indicator with interval switching are available.

On appliance of our isolating amplifiers KFA6...Ex1/ ...Ex2 the operating medium with type of protection intrinsic safety i. It has the classification I2G EExia IIC T6 and is approved for the operation in areas subject to explosion hazards.
The isolating amplifiers must be installed outside of the explosion endangered areas. EC type examinations of the physical technical federal agency (PTB) about the intrinsic safety of the applied slot initiators and isolating amplifiers exists. Slot initiators in safety technology are deliverable optionally.
For each limit value a two-core control cable is necessary. The allowed cable length between limit signal indicator and the after switch unit is according to PTB approximately 3 km, taking into account the intrinsic safety. The without contact working inductive limit signal indicators are also able for the
application in liquid-filled measurement devices.

Technical Data ( I )

Nominal voltage:8 V DC (Ri ~ 1 kOhm)
Operating voltage:5 - 25 V DC
Current input:≥ 3 mA  (active area free),
≤ 1 mA  (active area covered)
Ambient temperature:    -20°C to +70°C bzw. respectively
according to the particular
measuring device characteristics.
Switching accuracy:ca. 0,5% of the scale end value.

3. Pneumatic limit value indicators ( P )

Mode of operation and application
Pneumatic limit signal indicators are absolute explosion-proof (also appropriate for zone 0) and are working without contact. Like the inductive limit signal indicators they stand out by a high switching accuracy and also are highly insensitive
against vibrations and shocks.
The switching function can be easily reversed.
The jet-collector nozzle system is located at the carrier arm that is coneccted with the nominal value pointer, while the control flag is moved by the actual value pointer.
In this system a throttled, constantly streaming airflow is conducted from the jet nozzle in the collector nozzle. The low-pressure signal (>25 mbar) that is affiliated by the
collector nozzle is conducted to the pre-amplifier [connection
77(E)] of the low-pressure switch. This causes that a
micro switch is connecting the control connections 3 and 4 and therfore creates a switching effective output signal of 1,4 bar at the output 3. As the actual value pointer reaches the limit value pointer, the control flag that is taken along
by the actual value pointer, interrupts the air stream in the jet-collector nozzle system. Because of the absence of the low-pressure signa at the per-amplifier the switch is now activated. The micro-switch returns to the initial position
and de-aerate connection 3 through connection 5.
Instead of the pneumatic lof-pressure switch (PP-Wandler) an electro/pneumatic converter (PE-transducer) can beapplied. This is  recommended on combinations of pneumatic
and electric devices and on the monitoring of signals across larger distances to avoid delays.
The PP-transducer is openly mounted on the housings back side and is lowering the type of enclosure protection of the measuring device if applicable. In liquid-filled devices pneumatic limit value indicators cannot function (airstream!)

Pneumatic limit signal indicator

Technical Data ( P )

Converter:PP-transducer (optional PE-transducer)
Air consumption:<30 l/h / PP-transducer: < 40 Nl/h
bei 1,4 bar
Operating pressure:1,4 bar ± 0,1bar / PP-transducer: 1,4 bar ± 0,2 bar
Purity requirements
control pressure:      
≤ 0,04 mm
mech. durability:     PP-Wandler: 10⁸ Schaltspiele

Special constructions:
electric limit signal indicators on demand.

We reserve the right to alter technical data.

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