The sample gas is fed into an optical cell by a maintenance-free membrane pump. A beam of UV light passes through the optical cell, a part of it is absorbed by the mercury atoms present in the sample.
This method is called “atomic absorption spectroscopy” or shortly AAS. It is extremely selective and sensitive. For mercury determination the AAS method has maintained its importance even if other methods have been worked out since the early beginnings. The AAS method is low in interference and does not require an amalgamation step or expensive carrier gases.
The VM-3000 uses a high-frequency driven electrodeless low pressure mercury lamp (EDL) as UV source. This lamp emits lines of an extremely narrow bandwidth which are congruent with the absorption lines of the Hg atoms. Cross-sensitivities are thus minimized.
The extremely high stability of the UV source in the VM 3000 is a result of the reference beam feedback control method. Total background noise is less than 0.1 µg/m³.
The lamp unit and detectors are temperature stabilzed to avoid temperature drift. Heating of the optical cell renders the VM-3000 insensitive to water vapor.
Display and output of measurements
The result of a measurement is displayed in real time and output as an analogue electrical signal of 4-20 mA. The device also features digital outputs for alarm, status and measurement values for full integration in plant control systems as well as a serial interface (RS 232 / USB) for data transfer to a PC or Laptop (Software „Hg-Transfer“ included on delivery).
Thanks to the built-in p- and T-sensors the Hg-concentration can be output as μg/Nm³ (μg/cubic metre at normal temperature and pressure).
The easy to carry VM-3000 is well suited for indoor and outdoor mobile use.
Sources of mercury contamination or leakage are easily found. To that purpose an integrated 12 VDC battery pack (with charger) and a sampling probe are available as options.
Alternatively, the VM-3000 can be run on an external 12 VDC power source.
For prevailing mobile use we recommend the specially designed Tracker-3000 XS.
The VM-3000 can be combined with a multiplexer unit for automatic monitoring of several different measurement points.
For further information see procuct page Mercury Monitoring System (MMS).