MilliGascounters

Features

  • Minimum flow rate 1 ml/h
  • Maximum flow rate 1 ltr/h
  • Resolution 3 ml
  • Accuracy ±3 % of reading across full flow rate range; in combination with »RIGAMO« software better than ±1 %
  • Use with inert and medium corrosive gases (biogas) as well as highly aggressive gases
  • Materials: Plexiglas (PMMA), PVDF, PVC (red)
  • Digital counter with programmed calibration factor
  • Battery operated; battery life-time 3-4 years
  • Low-maintenance

Application

RITTER MilliGascounters (1) (MGC) are designed for the volumetric measurement of the smallest amounts of gas with ultra-low flow rates. They are suitable for measurement of all inert, slightly corrosive gases such as biogas (PMMA model) and aggressive gases (PVDF model). Furthermore, MilliGascounters can be used for volumetric leak detection.

(1) Developed at the University of Applied Sciences Hamburg, Prof. Dr. Paul A. Scherer

Advantages

  • Individual volumetric calibration of each MilliGascounter traceable to the German National Primary Standard (PTB)
  • Total gas production measured (instead of Methane only)
  • Head space volume of fermentation bottle at measurement start (= air) not erroneously measured as pure methane volume
  • No false readings due to CO2 absorption by combination of acidulated packing liquid and software correction

Measurement Priciple with Schematic

Das zu messende Gas gelangt über den Gaseingangsstutzen (3) durch eine Mikrokapillare (9) von unten in den Flüssigkeitsbehälter des MilliGascounters, der mit einer Sperrflüssigkeit (12) gefüllt ist.

Das Gas steigt in Form von kleinen Gasblasen innerhalb der Sperrflüssigkeit nach oben in die Messzelle (13). Die Messzelle besteht aus zwei Messkammern, die alternierend durch die aufsteigenden Gasblasen gefüllt werden. Nach erfolgter Füllung einer Messkammer kippt die Messzelle durch den Auftrieb der gefüllten Messkammer in eine Position, in der die gefüllte Messkammer entleert wird und die Füllung der zweiten Messkammer beginnt.

Die Volumenmessung des Gases erfolgt also in diskreten Schritten durch Zählung der Kippvorgänge der Messzelle (13) mit einer Auflösung von ca. 3 ml (= Inhalt einer Messkammer, siehe Ziff. 3.2 der MGC Bedienungsanleitung). Bei einer Abschätzung/Berechnung des Gesamt-Messfehlers ist dieser durch die Auflösung bedingte „Restfehler" (= max. 3 ml) zu berücksichtigen.

Der Kippvorgang löst über einen Permanent-Magneten (11) und einen der beiden Magnetsensoren (Reedkontakte) (10) einen Impuls aus, der vom Zählwerk (1) registriert wird.

Die Schaltimpulse des zweiten Reedkontaktes können über die Buchse (2) erfasst werden (siehe Ziff. 4.3 der MGC Bedienungsanleitung).

Das gemessene Gas entweicht durch den Gasausgangsstutzen (4).

Legende

  1. Zählwerk mit LCD-Anzeige
  2. Signal Ausgang (Reedkontakt)
  3. Gas Eingang
  4. Gas Ausgang
  5. Entlüftungsschraube für Befüllung
  6. Gas-Eingangskanal
  7. Gehäuse
  8. Bodenplatte
  9. Mikrokapillare
  10. Zwei Reed-Kontakte
  11. Permanent-Magnet
  12. Sperrflüssigkeit
  13. Messzelle (Kippkörper) mit Zwillings-Messkammern
  14. Makierungs-Schraube für Pegelstand (nur bei MilliGascounter MGC-1 PMMA)
  15. Revisionsschraube Gaskanal

Measuring-Range

The minimum flow rate is theoretically zero ltr/h as there are no mechanical limitations with the MilliGascounter which would define a minimum flow. However, at such micro flow rates there are external influences becoming evident: temperature and pressure variation, tightness of the hose connection, permeability of the gas inlet hose. Therefore, the minimum flow rate was defined as 1 ml/h. The maximum flow rate is 1.0 ltr/h.

Accuracy

Because of the physical measurement principle, the measurement error is dependent on the flow rate and it rates ±3% across the full flow rate range. Each MGC is individually calibrated at the standard flow rate of 0.5 ltr/h so that the measurement error is approx. 0% at this flow rate. At minimum flow rate the measurement error is approximately +3%, at maximum flow rate approximately -3%. The »RIGAMO« software (available as accessory) provides an algorithm which automatically recalculates the actual measurement data into the real volume at the respective actual flow rate on the basis of the calibration curve. The remaining error is smaller than ±1% across the full flow rate range.

Performance Data

Minimum flow Qmin 1 ml
Maximum flow Qmax 1 ltr/h
Measurement accuracy (1) ±3 | ±1 %
Measuring drum volume, approx (2) 3 ml
Min. measuring volume (resolution) (3) 3 ml
Packing liquid quantity, approx 120 ml
Diameter 98 mm
Height 109 mm
Weight 450 to 600 g
Maximum gas inlet pressure 100 mbar
Minimum gas inlet pressure 8 mbar
Gas inlet pressure at start of measurement (5) 9 mbar
Gas Temperature (4) 10 to 60 / 80 / 40 °C
Minimum dial division (6) 0.01 ml
Maximum indication value (6) 999,999.99 ml
Connection gas in/outlet PVDF screw-type tube coupling
Outside-Ø 6 mm
Inside-Ø 4 mm
  • (1) Because of the physical measurement principle, the measurement error is dependent on the flow rate. The data acquisition software »RIGAMO« (accessory) provides an algorithm, which auto- matically recalculates the actual measurement data to the real values at the respective actual flow rate on the basis of the calibration curve. Thus, the remaining error can be reduced significantly or the flow rate range can be extended at the constant measurement error of ±3%. The remaining error is better than approx. ±1% across the full flow rate range.
  • (2) = Nominal value; exact value will be determined by individual calibration
  • (3) = Volume of measuring chamber
  • (4) Max. Operating temperature for PMMA/PVDF/PVC. For complete MGC unit applies: With temperatures > room temperature (e.g. if placed in heating furnace) a foam formation of the packing liquid was monitored in particular cases.
  • (5) The minimum gas inlet may be increased if the measurement starts with a high flow rate. In this case a higher pressure is needed until the micro capillary in the base plate is clear of packing liquid.
  • (6) Because of calibration factor with 2 decimals

Display, Signal Output

The volume of the measured gas is displayed on the electronic digital display located on top of the MGC casing. Additionally a floating reed contact can be used as a signal output.

Data Acquisition with PC

For data acquisition of gas volume and flow rate the Windows software »RIGAMO« is available. The data of up to 24 Ritter gas meters can be transmitted to the USB port of a PC.

Available Models (Materials)

The MGCs are available in the following casing/measurement cell materials:

  • PMMA/PVDF
  • PVDF/PVDF
  • PVC-red/PVC-red

Standard Equipment

  • Twin-chamber measurement cell
  • Pulse Generator V6.0 (Reed Contact) , as signal output (floating output)
  • LCD Display , resettable, 8-digit
  • Level
  • Gas connection hose (PVC), 1.5 m
  • Screw-type tube connection for connection tube:
  • Connection gas inlet/outlet:
  • Funnel , for filling of liquid
  • Packing liquid, 200 ml
  • Syringe , for fine adjustment packing liquid level
  • Cleaning rod for micro capillary , per each 1 to 5 MGC's

Accessories

  • HCl solution 1.8 vol% for gas mixtures with CO2
  • Available quantities: 100 / 200 / 500 / 1,000 / 5,000 ml
  • Silox for gas mixtures without CO2
  • Filter 0.45 micron for gas inlet tube
  • Back-pressure valve for gas inlet tube