Digester Gas Monitor

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RKI is proud to introduce our Digester Gas Monitor. Gas from waste digesters contains high levels of methane, CO2, and H2S, with little to no oxygen present. The RKI gas monitor checks for all these gases on a cyclic basis. A powerful air aspirator pulls a sample from up to 100 feet away. Since digester gas contains high humidity and high H2S, both of which can cause damage to sampling systems, the RKI Digester Gas Monitor is designed to handle these with no damage to the sampling system or sensors. The sample is filtered through a series of dirt, dust, and moisture stopping filters, and these filters are automatically blown back and cleaned out with fresh air at the end of each cycle.

Measurement time is just 4 minutes, taken at periodic cycles. Cycle time is selectable, with settings for cycle time of 1 hour, 4 hours, 8 hours, 24 hours, or 7 days. A cycle can also be initiated anytime by pressing a button. After each cycle, the sensors and sampling system are flushed with fresh air so as to minimize corrosion caused by the high H2S content. The system is fault tolerant minimizing the possibility of expensive repairs or downtime.

System integrity is maintained at all times using a flow fail monitoring device which provides a fail alarm and relay if there is ever a problem with the flow system, such as a blockage, or if the air aspirator compressed air supply is removed or interrupted.

The system is housed in a wall mounting NEMA 4X enclosure. The gas readings can be viewed through the enclosure door clear window. Flow meters and filters are easily visible for confirmation of correct flows and operation. The RKI Digester Gas Monitor contains adjustable alarm levels for each gas, and also programmable alarm relays. In addition, the unit provides 4-20mA signals for each gas concentration for connection to an external DCS, PLC, or other site control system. A Modbus output is also available. The outputs are the readings received from the last cycle taken.

  • Corrosion resistant design
    • External construction for extreme environments
    • Internal construction for extreme samples
  • Sample system for high humidity]
  • Accurately measure gas with high levels of H2S present
  • 100 ft. sample range
  • Up to 4 sensors:
    • Methane % Vol.
    • CO2 % Vol.
    • Oxygen % Vol.
    • H2S 0-1000 PPM (0-3000 or 0-5000 optional)
  • Self draining moisture trap
  • Back flush for sample line
  • Long life air aspirator (no moving parts)
  • Inside/outside location
  • NEMA 4X enclosure
  • Uses proven RKI technology
  • Modular design easy to maintain
  • Simple to operate
  • Wastewater Treatment Digesters
  • Biogas Methane
  • Animal Farms
RKI Controller UsedBeacon 410 with special firmware structured to meet product requirements.
Input Power100/115/220 VAC ± 10% or 24VDC
Enclosure• NEMA 4X enclosure with a window for viewing the gas readings on an LCD display, flow meter, and any other items which require visibility. • For indoor or outdoor use.
Sampling MethodAir Aspirator (compressed air source is required)
Sample Filtering• Internal water trap automatically drained after each detection cycle with a 30 second blowback purge. • Internal gas dryer to dry the sample after it leaves the hydrophobic in line filter.
Flow RateSystem flow rate 3 SCFH.
Flow Meters0 – 5 SCFH Flow meter for total flow. 0 – 0.5 SCFH Flow meter with valve for H2S sample flow. 0 – 2 SCFH Flow meter with valve for H2S dilution flow.
Maximum Inlet/Exhaust

Tubing Length

100 ft.
Response TimeT90 in 30 seconds when gas applied directly to sample in fitting during test cycle.
Target Gases/Detection


• Methane: 0 – 100 % Volume • Oxygen: 0 – 25% Volume • CO2: 0 – 50% Volume • H2S: 0 – 1000 PPM using internal dilution (optional 0 – 3000 and 0 – 5000PPM range)
Sensors• Methane and CO2: NDIR (non-dispersive infrared) sensors • Oxygen and H2S: Long life electrochemical sensor
Operating Temperature/Humidity• 0°C – 40°C (32°F – 104°F) • 0 – 100% Relative Humidity
Alarms• Visual LED alarms (viewed through window) • Audible buzzer alarm (on housing bottom) • Optional loud horn/strobe alarm (on housing top)
Outputs• 4-20 mA for each active sensor • Modbus RTU RS-485
Size24”H x 24”W x 10”D (61cm H x 61cm W x 25.4cm D)
Wire EntryThree 3/4” Conduit Hubs on bottom of enclosure
Warranty1 Year

Note: Specifications subject to change without notice.

Digester Gas Monitor Literature

Product DatasheetManuals

Sample Draw Sensor / Transmitter 

Direct Connect Manual 
Operator’s Manual

Direct Connect Manual 
Maintenance Manual