Danfoss AKS 41 Liquid Level Transmitter
Publication 9-45
Section 9
Page 4 of 18
Issue 1 : 10/11
2.
Application
AKS 41 and AKS 41U liquid level transmitters are used to measure
refrigerant liquid level for control applications. The transmitter supplies a
4 to 20 mA signal in proportion to the level of liquid refrigerant. This
signal can be used with a suitable controller to control the level of
refrigerant within a vessel. The Danfoss EKC 347 liquid level controller is
dedicated for use with the AKS 41 and AKS 41U.
The location of the liquid level transmitter and level controller can be
found from the system schematic flow diagram and in Part A :
Specification in Section 1 of the plant instruction manual.
This publication is applicable to the latest version of the AKS 41 and AKS
41U fitted with one green LED. Information about the earlier version,
fitted with one green and one red LED, can be found in Appendix 1.
3.
Operation
The transmitter comprises consists of two parts: an inner insulated
electrode and an outer tube with a space between, forming a capacitive
rod. Liquid refrigerant flows up between the tube and the electrode; the
length immersed in the liquid is registered and transmitted as a 4 to
20 mA signal. The principle of operation is illustrated and described in
Fig 1.
In its simplest form, an electrical capacitor consists
of two conducting plates insulated from each other.
In this case the insulation medium is free-air.
When this example is translated to the capacitive
rod, the outer tube constitutes one plate and the
centre electrode the other plate.
Fig 1 Principle of Operation
Section through transmitter
(capacitive rod)
Electrode of
ordinary steel
Gap between the outer tube and
the insulated electrode where the
liquid can rise
Outer tube of stainless steel
Electrode hermetically
sealed in a non-conducting
PTFE material (Teflon)
