Gas Sensor Cross Sensitivity

This article describes gas cross sensitivity, how it can impact your gas sensors, and what gas sensors can exhibit it. The article applies to G7c, G7x, and G7 EXO.

What is gas sensor cross sensitivity?

Cross sensitivity is a phenomenon that occurs when a gas other than the gas being monitored causes the gas sensor to show a reading, even when the target gas is not present. An example of this would be an H₂S sensor responding to H₂ in the area.

What does Blackline do to alleviate cross sensitivity?

To alleviate cross sensitivity, Blackline:

Chooses sensors that are less likely to show a cross sensitive response
Includes filtration to remove the cross sensitive gases
Tests sensor and gas combinations to confirm the cross sensitive responses to other gases

What will I see During Calibration or Bump Testing when sensors are cross sensitive?

During calibration and bump testing a cross sensitive sensor, you will see readings on the sensor you are not calibrating or bump testing because the sensor has a response to the gas being applied during the calibration or bump testing.

What can I do when sensors get cross sensitive readings?

To reduce these cross sensitive responses, Blackline strongly recommends following the prescribed order of the gases applied to the device when doing either Dock or manual calibration or bump testing. For most sensor/gas combinations, the cross sensitive response can be removed by exposing the device to fresh air. Please consult with Customer Care for recommended fresh air exposure times.

What gas combinations produce noticeable cross sensitivity?

Almost all gases cause some cross sensitivity, but our devices are designed to filter out many of the most commonly occurring ones.

The following sensors can have cross sensitivity.


Sensor	Sensor Code	Notes on Cross-Sensitivities
Cl₂	L	Exposure to H₂S will poison the sensor; exposure to Cl₂ will reactivate the sensor. 20 ppm sample of SO₂ can cause 3.5 ppm reading. 1 ppm sample of Br can cause 1 ppm reading. 1 ppm sample of ClO₂ can cause 0.5 ppm reading. 1 ppm sample of F₂ can cause 0.4 ppm reading. 0.25 ppm sample of O₃ can cause 0.05 ppm reading.
ClO₂	W	20 ppm sample of H₂S can cause –5 ppm reading. 1 ppm sample of Cl₂ can cause 0.6 ppm reading. 0.25 ppm sample of O₃ can cause 0.7 ppm reading.
CO	M	200 ppm sample of H₂ can cause 25 ppm reading. 20 ppm sample of H₂S can cause <5 ppm reading. 50 ppm sample of NO can cause 25 ppm reading. 100 ppm sample of C₂H₄ can cause 100 ppm reading. Solvent vapors can poison sensors. Alcohols from de-icing fluids, bug repellent, hand sanitizers, aerosol cans, antiseptics, windshield washer fluid, engine coolant, and any other source of ethanol, methanol, or propanol can poison the sensor. Poisoned sensors can be repaired in the field. For more information, contact Blackline Safety Technical Support.
COSH (CO + H₂S) (North America and International)	D	CO Sensor: 100 ppm sample of H₂ can cause 20 ppm reading. 15 ppm sample of H₂S can cause 0–6 ppm reading. 35 ppm sample of NO can cause <0.1 ppm reading. 5 ppm sample of NO₂ can cause <0.1 ppm reading. H2S Sensor: 300 ppm sample of CO can cause <6 ppm reading. 100 ppm sample of H₂ can cause 0.03 ppm reading. 35 ppm sample of NO can cause <0.1 ppm reading. 5 ppm sample of NO₂ can cause –1 ppm reading. 5 ppm sample of SO₂ can cause <1 ppm reading. Alcohols from de-icing fluids, bug repellent, hand sanitizers, aerosol cans, antiseptics, windshield washer fluid, engine coolant, and any other source of ethanol, methanol, or propanol can poison the sensor. Poisoned sensors can be repaired in the field. For more information, contact Blackline Safety Technical Support.
COSH (CO + H₂S) (Europe)	5	CO Sensor: 25 ppm sample of H₂S can cause <5 ppm CO reading. 5 ppm sample of SO₂ can cause 0 ppm CO reading. 100 ppm sample of H₂ can cause < 30 ppm CO reading. 35 ppm sample of NO can cause <0.01 ppm CO reading. 5 ppm sample of NO₂ can cause <0.1 ppm CO reading. 15 ppm sample of Cl₂ can cause 0 ppm CO reading. H2S Sensor: 5 ppm sample of SO₂can cause <1 ppm H₂S reading. 100 ppm sample of H₂ can cause <0.05 ppm H₂S reading. 35 ppm sample of NO can cause <1 ppm H₂S reading. 300 ppm sample of CO can cause <5 ppm H₂S reading. 15 ppm sample of Cl₂ can cause 0 ppm H₂S reading. Alcohols from de-icing fluids, bug repellent, hand sanitizers, aerosol cans, antiseptics, windshield washer fluid, engine coolant, and any other source of ethanol, methanol, or propanol can poison the sensor. Poisoned sensors can be repaired in the field. For more information, contact Blackline Safety Technical Support.
CO-H	R	100 ppm sample of H₂ can cause –5 to 5 ppm reading. 15 ppm sample of H₂S can cause –0.5 to 0.5 ppm reading. 35 ppm sample of NO can cause 12 ppm reading. 5 ppm sample of NO₂ can cause <0.5 ppm reading. 100 ppm sample of C₂H₄ can cause 60 ppm reading. Solvent vapors can poison sensors. Alcohols from de-icing fluids, bug repellent, hand sanitizers, aerosol cans, antiseptics, windshield washer fluid, engine coolant, and any other source of ethanol, methanol, or propanol can poison the sensor. Poisoned sensors can be repaired in the field. For more information, contact Blackline Safety Technical Support.
High-range CO	T	100 ppm sample of H₂can cause 28 ppm reading. 48.6 ppm sample of NO can cause 14 ppm reading. 19.5 ppm sample of NO₂ can cause <0.5 ppm reading. 13.7 ppm sample of Cl₂ can cause <0.5 ppm reading. 100 ppm sample of C₂H₄ can cause 97 ppm reading. 100 ppm sample of C₂H₂ can cause 88 ppm reading. 100 ppm sample of C₂H₆ can cause 88 ppm reading. Solvent vapors can poison sensors. Alcohols from de-icing fluids, bug repellent, hand sanitizers, aerosol cans, antiseptics, windshield washer fluid, engine coolant, and any other source of ethanol, methanol, or propanol can poison the sensor. Poisoned sensors can be repaired in the field. For more information, contact Blackline Safety Technical Support. Note: Activated carbon filter cloth removes SO₂, NO₂, and H₂S, and provides short term (<1000 ppm hours) protection against methanol, ethanol, IPA.
High-range H₂S	J	100 ppm sample of CO can cause <2 ppm reading. Solvent vapors can poison sensor.
H₂	G	20 ppm sample of H₂S can cause 44 ppm reading. Note: Continuous high level exposure may reduce the efficiency of the filter material. C₂H₄ can affect reading. C₃H₈O can affect reading.
H₂ (North America)	7	25 ppm sample of H₂S can cause <2 ppm reading. 20 ppm sample of SO₂ can cause 0 ppm reading. 1000 ppm sample of CO can cause <300 ppm reading. 50 ppm sample of NO can cause <30 ppm reading. 20 ppm sample of NO₂ can cause 0 ppm reading. 50 ppm sample of Cl₂ can cause 0 ppm reading.
H₂S	H	100 ppm sample of CO can cause < 2 ppm reading. Solvent vapors can poison sensor.
HCN	N	Short gas exposure to H₂ in minute range; after filter saturation: approximately 40 ppm reading. 100 ppm sample of NO can cause –5 ppm reading. 10 ppm sample of NO₂ can cause –7 ppm reading.
LEL-MPS	F	CO₂ > 5000 ppm @ 1.75% LEL per 1000 ppm. Breathing directly into sensor can result in false LEL detection. Does not detect H₂S. O₂> 21.8%vol can result in 9.7% LEL. Single-gas calibration bottles with N₂balance (e.g., SO₂ balance N₂) will cause persistent cross readings and require a power cycle of the device. Exposing the MPS sensor to <10% O₂will cause erroneous readings and require a power cycle of the device.
NH₃	A	20 ppm sample of H₂S can cause 2 ppm reading.
High-range NH₃	B	5% sample of CO can cause –4 ppm reading. 20 ppm sample of H₂S can cause 5 ppm reading.
NO₂	K	15 ppm sample of H₂S can cause ~–1.2 ppm reading. 1 ppm sample of Cl₂ can cause 1 ppm reading. 0.8 ppm sample of O₃ can cause NO₂ readings adding up to 2.3 ppm after 30 seconds. After gas is stopped, the readings go back to zero after a minute. Solvent vapors can poison sensor.
O₂	O	Solvent vapors can poison sensor.
O₃	E	20 ppm sample of H₂S can cause –1.6 ppm reading; exposure >30 minutes can blind sensor. 10 ppm sample of NO₂ can cause 6 ppm reading; 10 ppm can cause over limit. After gas is stopped, O₃readings to to under limit, then back to zero after a few seconds. 1 ppm sample of Cl₂ can cause 1.2 ppm reading. Br can affect reading. I₂ can affect reading. 1 ppm sample of ClO₂ can cause 1.5 ppm reading.
PID	V	CH₄can decrease accuracy. C₂H₆ can decrease accuracy. Note: Sensor accuracy decreases with increased relative humidity and temperature, and exposure of the sensor to very humid, acidic (sour) and salty environments. This may cause inorganic salts to accumulate on PID enclosure walls, which ultimately compromises the screening potential of the MiniPID 2 fence electrode.
SO₂	S	300 ppm sample of CO can cause <1 ppm reading. 400 ppm sample of H₂ can cause <1 ppm reading. 25 ppm sample of H₂S can cause <0.1 ppm reading. 50 ppm sample of NO can cause 0–5 ppm reading. 6 ppm sample of NO₂ can cause < –10 ppm reading. 5 ppm sample of Cl₂ can cause < –2 ppm reading. 50 ppm sample of C₂H₄ can cause <45 ppm reading. 10 ppm sample of C₂H₂ can cause <30 ppm reading. 100 ppm sample of C₂H₆ can cause <30 ppm reading. Solvent vapors can poison sensor.

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