LEL-MPS Sensor Technical Notes
This article provides an overview of the operation, configuration, and performance of Blackline Safety's Molecular Property Spectrometer (MPS™) digital combustible gas sensor.
Overview
The MPS sensor is designed to detect and classify combustion gases.
Combustion gas classifications are based on the molecular weight of each gas detected. Overall combustion gas concentrations are displayed in %LEL (Lower Explosive Limit) on G7, G8, or EXO's screen.
Blackline gas logs can provide gas detection data based on classification and concentration, as detected by the MPS sensor.
How the Sensor Works
The MPS sensor uses proprietary technology to measure and report concentrations of the most common hydrocarbon combustible gases. This sensor also uses the thermodynamic properties of sample gases to categorize each gas into one of the six combustible gas classifications below:
Class 1: Hydrogen
Class 2: Hydrogen and hydrocarbon mixture
Class 3: Methane or natural gas
Class 4: Light gas or light gas mixture (ethane, propane, butane, isopropanol)
Class 5: Medium gas or medium gas mixture (pentane or hexane)
Class 6: Heavy gas or heavy gas mixture (toluene or xylene)
Calibration and Gas Selection
The MPS sensor uses methane as the bump and calibration gas.
Recommended Calibration Gas Composition
Blackline recommends 2.5% volume, 50% LEL methane.
Alternative Calibration Gas Composition
MPS sensor bump and calibration tests can also be completed using 2.2% volume, 44% LEL methane.
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.
If you are using 2.2% vol CH4, ensure that you update your device’s configuration profile in Blackline Live. For more information, see Methane Comparison (2.5% vs. 2.2%).
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Must contain at least 18% vol oxygen (O2).
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Can contain toxic gases.
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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:
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Must indicate that air is used as the balance gas (e.g., sulfur dioxide (SO2) with a balance of air, isobutylene with a balance of air).
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Must not use N2 as the balance gas.
If the gas cylinder used for either bump testing or calibration does not contain the correct balance gases, the MPS sensor will fail the bump test or calibration. In this case, the sensor may indicate an incorrect LEL value until the device is power cycled.
Sensor Accuracy
Operating Range
The MPS sensor has a broad operating range across temperature, relative humidity, and pressure metrics:
Temperature range: –20°C (–4°F) to +55°C (131°F)
Relative humidity range: 0% to 90% (non-condensing)
Barometric pressure range: 80–120 kPa (11.6–17.4 psi)
Detection Range
The sensor has a detection range of 4% to 100% LEL.
Sensor Reliability
Specific factors can impact the MPS sensor's performance, accuracy, and reliability:
Oxygen concentration: <10% of atmospheric oxygen by volume.
Temperature: >85°C (185°F).
Moisture: Water ingress into the sensor.
Safety
Safety Rating
The sensor is rated as intrinsically safe.
MPS Alarm Response
The MPS sensor is highly sensitive and responds quickly to the presence of several common combustible industrial gases.
All sensor alarms should be treated as exposure events and acted upon accordingly.
For additional safety guidelines at your location, contact your company's health and safety team or industrial hygienist.
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 affect the sensor's ability to accurately detect other combustible gases.
Contact Blackline Safety Technical Support prior to performing a manual calibration on an MPS sensor.