T4x a Compliance 4-gas monitor 

It is vital to ensure that the gas sensor you employ is fully optimised and reliable in the detection and accurate measurement of flammable gas and vapours, whatever environment or workplace it is within, is of the utmost importance. 

Fixed or portable? 

Gas detectors come in a range of different forms, most commonly they are known as fixed, portable or transportable, in which these devices are designed to meet the needs of the user and environment whilst protecting the safety of those within it.  

Fixed detectors are implemented as permanent fixtures within an environment to provide ongoing monitoring of plant and equipment. According to guidance from the Health and Safety Executive (HSE) these types of sensors are particularly helpful where there is the possibility of a leak into an enclosed or partially enclosed space which could lead to the accumulation of flammable gases. The International Gas Carrier Code (IGC Code) states that gas detection equipment should be installed to monitor the integrity of the environment that it is to monitor and should be tested in accordance with the recognised standards. This is to ensure that the fixed gas detection system operates effectively, timely and accurate calibration of the sensors is critical. 

Portable detectors normally come as a small, handheld device that can be used within smaller environments, confined spaces, to trace leaks or early warnings to the presence of flammable gas and vapour within hazardous areas. Transportable detectors are not handheld, but they are easily moved from place to place to act as a monitor ‘stand-in’ whilst a fixed sensor is undergoing maintenance. 

What is a compliance 4-gas monitor? 

Gas sensors are primarily optimised for detecting specific gases or vapours through design or calibration. It is desirable that a toxic gas sensor, for example one detecting carbon monoxide or hydrogen sulphide, provides an accurate indication of the target gas concentration rather than a response to another interfering compound. Personal safety monitors often combine several sensors for protecting the user against specific gas risks. However, a ‘Compliance 4-Gas monitor’ comprises sensors for measuring levels of carbon monoxide (CO) hydrogen sulphide (H2S), oxygen (O2) and flammable gases; normally methane (CH4) in one device.  

The T4x monitor with the ground-breaking MPS™ sensor is able to provide protection from CO, H2S, O2 risks with accurate measurement of multiple flammable gases and vapours utilising a basic methane calibration. 

Is there a need for a compliance 4-gas monitor? 

Many of the flammable gas sensors deployed in conventional monitors are optimized for detecting a specific gas or vapour through calibration but will respond to many other compounds. This is problematic and potentially dangerous as the gas concentration indicated by the sensor will not be accurate and may indicate a higher (or more dangerously) and lower concentration of gas/vapour than is present. With workers often potentially exposed to risks from multiple flammable gases and vapours within their workplace, it is incredibly important to ensure that they are protected through the implementation of an accurate and reliable sensor. 

How is the T4x portable 4-in-1 gas detector different? 

To ensure ongoing reliability and accuracy of the T4x detector. The detector utilises the  MPS™ (Molecular Property Spectrometry) Sensor functionality within its robust unit that provides a range of features to ensure safety. It offers protection against the four common gas hazards: carbon monoxide, hydrogen sulphide, flammable gases and oxygen depletion, whilst The T4x multi gas detector now comes with improved detection of pentane, hexane and other long chain hydrocarbons. It comprises a large single button and easy-to-follow menu system to enable ease of use for those wearing gloves, who’ve undergone minimal training. Tough, yet portable, the T4x detector features an integrated rubber boot and an optional clip-on filter that can be easily removed and replaced when needed. These features allow the sensors to remain protected even within the dirtiest environments, to ensure they can constant. 

A unique benefit to the T4x detector is that it ensures toxic gas exposure is calculated accurately throughout an entire shift, even if it is switched off momentarily, during a break or when travelling to another site. The TWA feature allows for uninterrupted and disrupted monitoring, So, when powering up, the detector begins again from zero, as if starting a new shift and ignores all previous measurements. The T4x allows the user the option to include previous measurements from within the correct time frame. The detector is not just reliable in terms of accurate detection and measurement of four gases, it is also dependable due to its battery life. It lasts for 18 hours and is useful for usage across multiple or longer shifts without requiring charging as regularly.  

During usage the T4 employs a handy ‘traffic light’ display offering constant visual assurance that it is operating soundly and conforming to the site bump test and calibration policy. The bright green and red Positive Safety LEDs are visible to all and, as a result, offer a quick, simple and comprehensive indication of the monitor’s status to both the user and others around them. 

T4x helps operations teams focus on more value adding tasks by reducing the number of sensor replacements by 75% and increasing sensor reliability. Through ensuring compliance across site T4x helps health and safety managers by eliminating the need to ensure each device is calibrated for the relevant flammable gas as it accurately detects 19 at once. Being poison resistant and with battery life doubled, operators are more likely to never be without a device. T4x reduces the 5-year total cost of ownership by over 25% and saves 12g of lead per detector which makes it much easier to recycle at the end of its life. 

Overall, through the combination of three sensors (including two new sensor technologies MPS and Long-life O2) within an already popular portable multi-gas detector. Crowcon allowed for the enhancement of safety, cost-effectiveness and efficiency of individual units and entire fleets. The new T4x offers longer life with a higher accuracy for gas hazard detection whilst providing a more sustainable build than ever before. 

How Long will my Gas Sensor Last?

Gas detectors are used extensively within many industries (such as water treatment, refinery, petrochemical, steel and construction to name a few) to protect personnel and equipment from dangerous gases and their effects. Users of portable and fixed devices will be familiar with the potentially significant costs of keeping their instruments operating safely over their operational life. Gas sensors are understood to provide a measurement of the concentration of some analyte of interest, such as CO (carbon monoxide), CO2 (carbon dioxide), or NOx (nitrogen oxide). There are two most used gas sensors within industrial applications: electrochemical for toxic gases and oxygen measurement, and pellistors (or catalytic beads) for flammable gases. In recent years, the introduction of both Oxygen and MPS (Molecular Property Spectrometer) sensors have allowed for improved safety.  

How do I know when my sensor has failed? 

There have been several patents and techniques applied to gas detectors over the past few decades which claim to be able to determine when an electrochemical sensor has failed. Most of these however, only infer that the sensor is operating through some form of electrode stimulation and might provide a false sense of security. The only sure method of demonstrating that a sensor is working is to apply test gas and measure the response: a bump test or full calibration. 

Electrochemical Sensor  

Electrochemical sensors are the most used in diffusion mode in which gas in the ambient environment enters through a hole in the face of the cell. Some instruments use a pump to supply air or gas samples to the sensor. A PTFE membrane is fitted over the hole to prevent water or oils from entering the cell. Sensor ranges and sensitivities can be varied in design by using different size holes. Larger holes provide higher sensitivity and resolution, whereas smaller holes reduce sensitivity and resolution but increase the range. 

Factors affecting Electrochemical Sensor Life 

There are three main factors that affect the sensor life including temperature, exposure to extremely high gas concentrations and humidity. Other factors include sensor electrodes and extreme vibration and mechanical shocks.  

Temperature extremes can affect sensor life. The manufacturer will state an operating temperature range for the instrument: typically -30˚C to +50˚C. High quality sensors will, however, be able to withstand temporary excursions beyond these limits. Short (1-2 hours) exposure to 60-65˚C for H2S or CO sensors (for example) is acceptable, but repeated incidents will result in evaporation of the electrolyte and shifts in the baseline (zero) reading and slower response. 

Exposure to extremely high gas concentrations can also compromise sensor performance. Electrochemical sensors are typically tested by exposure to as much as ten-times their design limit. Sensors constructed using high quality catalyst material should be able to withstand such exposures without changes to chemistry or long-term performance loss. Sensors with lower catalyst loading may suffer damage.  

The most considerable influence on sensor life is humidity. The ideal environmental condition for electrochemical sensors is 20˚Celsius and 60% RH (relative humidity). When the ambient humidity increases beyond 60%RH water will be absorbed into the electrolyte causing dilution. In extreme cases the liquid content can increase by 2-3 times, potentially resulting in leakage from the sensor body, and then through the pins. Below 60%RH water in the electrolyte will begin to de-hydrate. The response time may be significantly extended as the electrolyte or dehydrated. Sensor electrodes can in unusual conditions be poisoned by interfering gases that adsorb onto the catalyst or react with it creating by-products which inhibit the catalyst.  

Extreme vibration and mechanical shocks can also harm sensors by fracturing the welds that bond the platinum electrodes, connecting strips (or wires in some sensors) and pins together.  

‘Normal’ Life Expectancy of Electrochemical Sensor 

Electrochemical sensors for common gases such as carbon monoxide or hydrogen sulphide have an operational life typically stated at 2-3 years. More exotic gas sensor such as hydrogen fluoride may have a life of only 12-18 months. In ideal conditions (stable temperature and humidity in the region of 20˚C and 60%RH) with no incidence of contaminants, electrochemical sensors have been known to operate more than 4000 days (11 years). Periodic exposure to the target gas does not limit the life of these tiny fuel cells: high quality sensors have a large amount of catalyst material and robust conductors which do not become depleted by the reaction. 

Pellistor Sensor 

Pellistor sensors consist of two matched wire coils, each embedded in a ceramic bead. Current is passed through the coils, heating the beads to approximately 500˚C. Flammable gas burns on the bead and the additional heat generated produces an increase in coil resistance which is measured by the instrument to indicate gas concentration. 

Factors affecting Pellistor Sensor Life 

The two main factors that affect the sensor life include exposure to high gas concentration and poising or inhibition of the sensor. Extreme mechanical shock or vibration can also affect the sensor life. The capacity of the catalyst surface to oxidise the gas reduces when it has been poisoned or inhibited. Sensor life more than ten years is common in applications where inhibiting or poisoning compounds are not present. Higher power pellistors have greater catalytic activity and are less vulnerable to poisoning. More porous beads also have greater catalytic activity as their surface volume in increased. Skilled initial design and sophisticated manufacturing processes ensure maximum bead porosity. Exposure to high gas concentrations (>100%LEL) may also compromise sensor performance and create an offset in the zero/base-line signal. Incomplete combustion results in carbon deposits on the bead: the carbon ‘grows’ in the pores and creates mechanical damage. The carbon may however be burned off over time to re-reveal catalytic sites. Extreme mechanical shock or vibration can in rare cases also cause a break in the pellistor coils. This issue is more prevalent on portable rather than fixed-point gas detectors as they are more likely to be dropped, and the pellistors used are lower power (to maximise battery life) and thus use more delicate thinner wire coils. 

How do I know when my sensor has failed? 

A pellistor that has been poisoned remains electrically operational but may fail to respond to gas. Hence the gas detector and control system may appear to be in a healthy state, but a flammable gas leak may not be detected. 

Oxygen Sensor 

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Our new lead-free, long-lasting oxygen sensor does not have compressed strands of lead the electrolyte has to penetrate, allowing a thick electrolyte to be used which means no leaks, no leak induced corrosion, and improved safety. The additional robustness of this sensor allows us to confidently offer a 5-year warranty for added piece of mind. 

Long life-oxygen sensors have an extensive lifespan of 5-years, with less downtime, lower cost of ownership, and reduced environmental impact. They accurately measure oxygen over a broad range of concentrations from 0 to 30% volume and are the next generation of O2 gas detection. 

MPS Sensor  

MPS sensor provides advanced technology that removes the need to calibrate and provides a ‘True LEL (lower explosive limit)’ for reading for fifteen flammable gases but can detect all flammable gases in a multi-species environment, resulting in lower ongoing maintenance costs and reduced interaction with the unit. This reduces risk to personnel and avoids costly downtime. The MPS sensor is also immune to sensor poisoning.  

Sensor failure due to poisoning can be a frustrating and costly experience. The technology in the MPS™ sensor is not affected by contaminates in the environment. Processes that have contaminates now have access to a solution that operates reliably with fail safe design to alert operator to offer a peace of mind for personnel and assets located in hazardous environment. It is now possible to detect multiple flammable gases, even in harsh environments, using just one sensor that does not require calibration and has an expected lifespan of at least 5 years.