PKG 4-20

• for remote transmission of liquid levels using 
  the air bubbler method

• with immersion bell made of stainless steel

Area of application

The PKG 4-20 liquid level transmitter with accessories is suitable/not suitable for use in the
following liquids and/or the following areas:

Suitable for use:
- in clean, low-viscosity liquids (e.g. cooling water) through to soiled liquids with high solid
  content (e.g. milk of lime) in non-pressurised open tanks or shafts.

Not suitable for use:
- in liquids which, due to deposits, bonding or crystallisation, might prevent the injection of
  air into the immersion bell or immersion tube
- in liquids whose viscosity is so high that they do not allow the surplus air bubbles to
  escape through the liquid to the top
- in liquids with a tendency to foam
- in liquids that attack the materials used
- in liquid foodstuffs
- in contaminant liquids (as, if the air hose ruptures above the filling level, the suction action
  in the hose could allow contaminant liquids to escape)
- in liquids in tanks that are under pressure
- in dusty rooms (as installation site for the PKG 4-20 liquid level transmitter)
- in potentially explosive areas

Technical data:

Integrated in the housing:

Air pump
Supply voltage: AC 230 V; other supply voltage on request
Power consumption: max. 100 VA
Interval circuit: in operation for approx. 10 seconds,
in standstill mode for approx. 50 seconds

Pressure sensor
Supply voltage: DC 15 ... 30 V via separate voltage source SELV or PELV or
via MSU ... transducer or SKG 4-20 switching unit

Measuring range: as desired by the customer, but:
smallest measuring range 0 to 0.7 m water column (tolerance +/- 15 mm) -
largest measuring range 0 to 10 m water column (tolerance +/- 55 mm)

Measuring signal: load-independent current DC 4 ... 20 mA
The pressure sensor used is works-set so that the output signal 4 ... 20 mA corresponds 
to its entire measuring range. If, for application reasons, the entire measuring range of
the pressure sensor used should not correspond to the output signal 4 ... 20 mA, the range 
can be altered by intermediate connection of a MSU 420 or MSU 1020 transducer. 
The 0% value and the 100 % value can be redefined by adjusting two spindle trimmers.

The MSU 1020 transducer also permits conversion into the output signals 
0 ... 10 V and 0 ... 20 mA.

Extras:

Hose line:
Material and dimensions of hose line: PVC air hose, 6 x 4 mm Ø,
including a plastic “Y” connection piece
Length of hose line: 20 metres; other lengths on request

Immersion bell (for suspension mounting):
stainless steel 316 Ti or 316, approx. 101 mm Ø x 108 mm high,
mounted using 1 stainless steel hose connector and
1 stainless steel dummy plug, with 1 stainless steel hose connector as option, 
with 2 metres stainless steel rope of 3 mm Ø and 2 rope clips made of stainless steel; 
longer stainless steel rope on request

Length of hose line: 20 metres; other lengths on request

Available version of the immersion bell:

- PVC version (for wall mounting)
PVC, approx. 63 mm Ø x 200 mm high,
mounted using 1 hose connector and 1 dummy plug
and with 1 hose connector as option and with wall bracket made of galvanised steel

- Grey cast iron version (for suspension mounting)
grey cast iron, approx. 114 mm Ø x 100 mm high,
mounted using 1 hose connector and 1 dummy plug
and with 1 hose connector as option, 
with 2 metres stainless steel rope of 3 mm Ø and 2 rope clips made of stainless steel; 
longer stainless steel rope on request

- Stainless steel version (for suspension mounting) 
stainless steel 316 Ti or 316, approx. 101 mm Ø x 108 mm high,
mounted using 1 stainless steel hose connector and
1 stainless steel dummy plug, with 1 stainless steel hose connector as option, 
with 2 metres stainless steel rope of 3 mm Ø and 2 rope clips made of stainless steel; 
longer stainless steel rope on request


Alternative: immersion tube
PP version on request
Stainless steel 316 Ti version on request

Max. distance between housing and immersion bell or immersion tube: 100 m

Mode of operation

Due to the force of gravity and as a function of the specific gravity of the liquid, the pressure
at the bottom of a tank is proportional to the liquid level in the tank. The pressure
corresponding to the liquid level is measured by means of an immersion bell mounted just
above the bottom of the tank or an immersion tube which is open at the end and
suspended slightly above the bottom of the tank. An air pump integrated in the liquid level
transmitter pumps air into the bell or tube via a hose for 10 seconds every 50 seconds.
The air pressure at the bottom edge of the immersion bell or at the end of the immersion
tube following the injection of air is equal to the pressure generated by the liquid. 

The air pressure in the immersion bell or immersion tube is measured by a pressure sensor
integrated in the liquid level transmitter and converted into a load-independent current
signal of between 4 and 20 mA via an integrated current loop transmitter.


Installation and start-up

The units described in this documentation may only be installed, connected and
started up by suitably qualified personnel!

Installation of the PKG 4-20 liquid level transmitter:

The liquid level transmitter PKG 4-20 is designed for wall mounting. It is fastened in place
using 4 screws from the inside of the housing (see dimensional diagram PKG-420).
The electrical connections for the operating equipment may only be made after the
mechanical installation of the measuring system has been completed.

Installation of the immersion bell or immersion tube and the hose lines:
There are basically two ways to install the immersion bell/immersion tube and the hose lines:

Method 1

Description:
Joint air hose for air injection and measurement of pressure build-up

Advantages:
The joint air hose is purged with compressed air every 50 seconds. 
This ensures that no liquid can rise in the joint air hose and falsify the measurement value.

Disadvantages:
There is a short-term pressure build-up when the air pump is started up, and the 
measurement value therefore rises temporarily.

Recommendation: 
Preferred method: particularly with short hose lengths up to 20 metres and wherever 
fluctuations in measuring values are acceptable.


Method 2

Description:
One hose each for air injection and measurement of pressure build-up

Advantages:
In contrast to Method 1, there is no short-term pressure build-up when the air pump is started.
The measurement value remains almost stable.

Disadvantages:
The air hose for measurement of the built-up pressure is not purged, with the result that 
residues may form or the liquid may rise, leading to an incorrect measurement value.
The measuring system may not be shut down. In other words, you must ensure that there is
always an air cushion in the immersion bell to prevent liquid from rising in the air hose which 
is used to measure the built-up pressure.

Recommendation:
Only to be used where fluctuations in measuring values are to be kept to a minimum.


Whichever method is used, you must always ensure that the already in operation before 
the liquid is filled into the tank.