AMETEK Process Instruments

- Model Ranarex - Portable Gas Gravitometer



The Need : Plant and process operators need a reliable, simple means of confirming the quality or mixture of process gases. The means used to perform these tests must be reliable, accurate, and very affordable. For many processes and situations, gas quality can be easily inferred through a simple analysis of the gas mixture's specific gravity as opposed to a complex spectral analysis.

The Ranarex Portable Gas Gravitometer is an easy-to-use, fast responding gas gravitometer that is used to determine the specific gravity of a process gas as compared with air. This unit offers multiple scales and field-proven accuracy within .05% of actual value at any reading. Dual ranges are available: 0.52-1.03 and .097-1.90 relative density (specific gravity).

  • Accurate Eliminates span drift to ensure permanently accurate calibration.
  • Sensitive Advanced design develops large measuring forces and is virtually friction-free.
  • Fast Response Gas sample flows continuously at a high rate through a small measuring chamber that purges rapidly.
  • Rugged Durable, corrosion-resistant materials. Outer case protects against dust, humidity, and shock.
  • Low Cost Simple design for low equipment cost; simple piping and wiring for low installation cost; rugged construction for low maintenance cost. These features ensure lowest long-term, total cost.
  • Easy to Use Completely mechanical and easily understood. Installation requires only piping or tubing and electrical power. No special skills required.
  • Readable Indicating scale is 6” wide. Can be read from a distance.

The Ranarex principle and design are simple. The chassis of the gravitometer forms two cylindrical, gas-tight measuring chambers; each has a separate inlet and outlet connection. In each chamber there is an impeller and an impulse wheel, both with axial vanes. These wheels are mounted on separate shafts, facing each other but not touching. An electric motor and drive belt rotate the impellers at the same speed and in the same direction. The impellers draw continuous flow of gas sample into the upper chamber, and reference air into the lower chamber. They spin the gas and air against the vanes of the corresponding impulse wheels. As the spinning gas and air impinge against the vanes, they create torques on the impulse wheels that are proportional to the density of the gas and of the air.

Specific Gravity

These torques are transmitted from the chambers to two external measuring wheels. A flexible tape is wrapped on the measuring wheel rims in the crossed direction so that the torque creates two opposing forces. The measuring wheels are restrained from continuous rotation, but a difference between the torques allows limited motion of the entire system. The measuring system divides the torque of the gas by the torque of the air. This is the same ratio as the density of the gas divided by the density of the air which is —the specific gravity.

The rim of the gas measuring wheel is contoured so that it rotates through equal angles for equal changes in specific gravity. The uniform motion of the gas measuring wheel is transmitted by a link to the readout indicator.

To ensure accuracy, the gas sample and the reference air must be measured at ambient temperature, at barometric pressure, and at equal humidity content (either humidified or dry).

Portable Gravitometer

No elaborate setup is required for the portable version. The unit can be operated from the floor, a bench, or hung from the wall and operated from a standard AC power supply or from a 12-Volt vehicle battery through a DC-AC inverter.

  • Accuracy: ±0.5% of actual value
  • Readings: Indicating only.
  • Drive Motor: 115 VAC, 60 Hz or 230 VAC, 50 Hz
  • Sample Flow Rate: 10-15 Scf/hour
  • Sample Pressure: 20 psig maximum
  • Specific Gravity Range: Dual Scale: 0.52 to 1.03 and 0.97 to 1.90
  • Ambient Air Reference Dryer: Silica Gel
  • Flowmeter: Built-in sample gas flowmeter
  • Actual Weight:
    • 220v model: 46 pounds
    • 115v model: 38 pounds
  • Ship Weight: 50 lb (23 kg)

  • Power inverter: 12 VDC to 115 VAC or 230 VAC
  • Carrying case with handle
  • Protective treatment for sour gas applications

  • Oil Refining
  • Natural Gas Measurement
  • Gas Utilities
  • Chemical Processing
  • Heat Treating Metals
  • Combustion Analysis
  • Sewage Treatment

  • Instantaneous Response: No time required for chemical reaction or gas diffusion.
  • Excellent Reliability: Components positioned to equalize temperatures of gas sample and reference air during analysis.
  • No Chemicals to Replace: Jeweled pivots and permanently lubricated ball bearings minimize wear and virtually eliminate servicing.

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