LEL-MPS Sensor Technical Notes

Updated: September 26, 2022

This support article is a technical reference for some key topics related to NevadaNano Molecular Property Spectrometer (MPS™) combustible gas sensors.

For detailed information on MPS sensors, as well as an overview of combustible gas detection, refer to the Blackline Safety whitepaper Combustible Gas and its Detection.

INERT ENVIRONMENTS AND LOW OXYGEN

The MPS sensor is designed for detecting gas in real world environments and therefore depends on some oxygen in the atmosphere to function accurately.

Using MPS sensors when oxygen (O₂) levels are below 18% may negatively impact accuracy. Furthermore, Blackline does not recommend use using MPS sensors in environments where O₂ levels are below 10%. A similar limitation exists for pellistor (catalytic bead) sensor technology.

When using a G7 in inert environments with less than 10% oxygen, Blackline recommends using Nondispersive infrared (NDIR) sensors to detect combustible gases.

CALIBRATION VERIFICATION

By default, the calibration process for an MPS sensor will validate and ensure accuracy without adjusting the sensor readings. This sensor is factory calibrated for optimal accuracy and Blackline Safety recommends using the factory calibration for the lifetime of the sensor.

Advanced users can perform a full calibration with a span adjustment by configuring this in Blackline Live. This may negatively impact the ability of the sensor to accurately detect other combustible gases.

Please contact Blackline Customer Care prior to performing a manual calibration on an MPS sensor.

METHANE COMPARISON (2.5% VS. 2.2%)

As with all Blackline combustible gas sensors, 2.5%vol methane (CH₄) is considered 50 % ± 2 %LEL (according to IEC standard EN60079). Customers applying 2.2% methane to devices calibrated to 2.5%vol CH₄ will observe a reading of 44% LEL.

If you prefer that 2.2%vol CH₄ read as 50% ± 2 %LEL, update your device’s default configuration profile in Blackline Live to enable span adjustment, and then perform a calibration using 2.2%vol CH₄. Your device’s readings will be adjusted to display 50% ±2 %LEL.

GAS CYLINDER SELECTION

Multi-gas cylinders:

When bump testing or calibrating cartridges equipped with an MPS sensor using a multi-gas cylinder, the cylinder:

• Must contain 50% LEL methane (CH₄) and must not contain any other combustible gases (e.g., pentane, butane, propane) or hydrogen.
  NOTE: If you are using 2.2% vol CH₄, ensure that you update your device’s configuration profile in Blackline Live as outlined in the section above.

• Must contain at least 18%vol oxygen (O₂).
• Can contain toxic gases.
• Can use nitrogen (N₂) as the balance gas.

Single-gas cylinders:

When bump testing or calibrating cartridges equipped with an MPS sensor using a single-gas cylinder, the cylinder:

• Must indicate that air is used as the balance gas (e.g.’s, sulfur dioxide (SO₂) with a balance of air, isobutylene with a balance of air).
• Must not use N₂ as the balance gas.

If cylinders are used that do not contain the correct gas mixtures, the MPS sensor will fail the bump test or calibration and will indicate an incorrect LEL value until the device is power cycled.

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