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Digox 602 dac

DAC measurement has become an important basic parameter in the water-steam cycle; especially in the combined cycle of a peaking power plant. DAC measurement is recommended as standard in feed water and steam. Thanks to the DAC measurement, it measures the conductivity value without the influence of CO2, which significantly reduces the start-up time of the power plant. For power plant operators, this is not only an environmental benefit, but also an economic one.

Acid Conductivity

In a cation filter, H + from the exchanged cations are combined with OH- from the alkalizing agent to water. The remaining conductivity is determined by autoprotolysis of pure water plus impurities in the form of anions, i.e. CO3 2-.
For steam turbine operation, the acid conductivity must not exceed the threshold of 0.2 μS / cm.

The causes of increased conductivity can be the following:

  • dirty piping system, high corrosion conditions
  • cooling water leakage into the condenser
  • air leakage into the atmosphere with the impact of CO2
  • organic substances in the boiler feed water - the impact of CO2 after heating 

Degassed Cation Conductivity

For the shortest possible start-up phase, the conductive acid must be measured without affecting the conductivity caused by the dissolution of CO2. The threshold value for turbine operation is thus reached faster. Dissolved CO2 increases conductivity but does not damage the turbine.

Therefore, it is necessary to remove carbonic acid from the sample and measure the conductivity again (degassed acid conductivity). On the one hand, the start-up phase can be significantly shortened, on the other hand, organic matter and the ingress of atmospheric air can be monitored.

With Digox 602 dac, you have a universal measuring device available for this type of task. In the compact design, you have the first double conductivity measurement, including a cation filter, automatic deaeration and pH calculation according to VGB-S006, then the detachable operation of the degassing unit with conductivity measurement before and after degassing. Depending on the efficiency, degassing can be calculated at 100%.

Technical Specification


Digox 602 dac

Measuring range Conductivity 0 - 1000 μS / cm, pH calculation from 7.5 to 10.5


Graphic display, backlight, colour changes in messages


<[1% of measured value + 0.015 μS / cm]

Alarm outputs

One relay per unit: 3A / 250 VAC, 3A / 30 VDC, no inductive loads

Error messages

Flow / device error,  exceeded temperature on relay / error current: 22 mA


Password protection for a menu listed item using 7 control keys

Analogue outputs

4 output, 0 (4)… 20 mA, linear / bilinear, max. load 500 Ohm

Digital interface

Profibus DP

Ambient temperature

Ambient temperature +5 - 45 ° C, storage and transport 0 - 50 ° C, relative humidity 30 - 95%

Sample quatity

10 - 20 l / h CatControl-Unit, 3 - 5 l / h degassing unit, display in I / h with digital flow sensor 

Power source

90 - 264 VAC 50/60 Hz, 60 VA nebo 120 - 264 VDC, 60 VA

Protection system

IP 65 (elektrical parts)


27.5 kg


850 x 570 x 210 mm (height x width x depth)

Main Functions

  • Degassing and measuring of all conductivities at the same, not-increased sample temperature
  • No warming up, i.e. no gas emissions from other volatile acids
  • No inert gas needed, air conditioning by the means of air treatment
  • High yield of degassed carbonic acid
  • Very short response times t90 <90 s for the degassing unit
  • Regenerating process chemicals for cation exchange resin
  • Very low power consumption <60VA
  • Available as an optional equipment for existing cation conductivity measurements: Digox dac basic
  • Easy flow adjustment and stabilization using built-in flow stabilizer
  • Improved degassing efficiency> 90%, with switchable calculation to 100%
  • Highly accurate temperature and conductivity measurements
  • Profibus DP interface