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RT 681 Multivariable Control: Vacuum Degassing
Education / GUNT Hamburg / Process Engineering / Complex Process Engineering Control Systems /

With RT 681 the complexities of a multivariable control system can be learned in a practical manner. The model for the controlled process is a typical application from process engineering: separation of gas dissolved in liquid. The pressure falls below the vapour pressure of the dissolved gas in a vacuum tank, so that it passes into the gas phase and can be removed (desorption).

  The liquid used in RT 681 is water, and the gas is ambient air. A water jet pump generates the vacuum in the vacuum tank. The vacuum firstly draws water from a collecting tank into the vacuum tank. Secondly, ambient air is drawn in and mixed with the water before entering the vacuum tank. The water/air mixing ratio can be adjusted by way of rotameters and valves. The vacuum in the vacuum tank degasses the water again. A pump transports the water out of the vacuum tank back into the collecting tank. A control valve is used to influence the flow rate and thus the level in the vacuum tank. Another pump circulates water from the collecting tank to operate the water jet pump. A control valve adjusts the flow rate in this circuit. In this way the vacuum pressure in the vacuum tank is adjusted. The vacuum pressure and level are mutually dependent variables. It is this dependence that makes this multivariable control system so complex.

  Two industrial controllers are provided as level and pressure controllers. They can be configured and parameterised using a supplied software. The controllers have a Profibus DP interface. The interface permits monitoring of the trainer via an optionally available software RT 650.60. The RT 650.60 software also permits recording of the process variables and parameterisation of the controllers using the PC. It is also possible to interconnect multiple trainers from this series through the Profibus DP interface.


Learning Objectives / Experiments
- coupled level and pressure control
- level control with various controller types
- pressure control with various controller types
- plotting step responses

[1] coupled level and pressure control in one vacuum tank
[2] water circuit with vacuum tank, collecting tank, pump and ambient air input device
[3] water jet pump to generate a vacuum in the vacuum tank
[4] circuit with pump for operation of the water jet pump
[5] level control with pneumatic control valve as actuator
[6] pressure control with pneumatic control valve in the circuit for operation of the water jet pump
[7] level controller and pressure controller configurable and parameterisable with software 
[8] optional process control software RT 650.60 via Profibus DP interface


Technical Data

- vacuum tank: 19L
- collecting tank: 100L
2 centrifugal pumps
- max. flow rate: approx. 50L/min
- max. head: approx. 30m
Water jet pump: final vacuum: approx. 0,3bar
Temperature and level controller parameterisable as
- P, PI or PID controller
- switching controller

Measuring ranges
- pressure: -1...0,6bar
- level: 30...480mm

- flow rate: 1x 200...2.500L/h, 1x 0...360L/h


Dimensions and Weight
LxWxH: 1.150x700x1.970mm
Weight: approx. 115kg
Required for Operation
230V, 50Hz, 1 phase oder 120V, 60Hz, 1 phase
Compressed air connection for control valve: 2...10bar
Scope of Delivery

1 trainer

1 cable

1 hose

1 CD with software for parameterisation and

   configuration of the controllers
1 set of instructional material

Order Details

080.68100  RT 681 Multivariable Control:

                       Vacuum Degassing