Sensing Carbon Dioxide for Total Organic Carbon Monitoring

Organic carbon compounds are often specified in terms of carbon mass. Recent developments in TOC (total organic carbon) analysis have resulted in considerable improvements, which allow for complete and direct measurement of the quantity of carbon with a biological source. Where there are fluctuations and differences, the cause and effect on biological processes in waste water study can be identified.

The TIC (total inorganic carbon) is usually removed from a sample by means of acidification and purging prior to oxidizing the residual organic carbon in the water sample to carbon dioxide (CO2) and then quantifying the amount of CO2 generated (Figure 1).

Typical TOC Process

Figure 1. Typical TOC process

A number of techniques are available which can be used to oxidize the organic carbon, such as oxygen, UV radiation, wet chemistry, or heat to generate CO2. Regardless of the method, the resulting CO2 is dissolved in a carrier gas, such as oxygen. This carrier gas is passed via the Edinburgh Sensors’ NDIR gas sensor to determine the CO2 content. When CO2 concentration is higher, the TOC level will also be higher and the water sample will be more contaminated.

Based on the cleanliness of the water being analyzed and the methods utilized, different concentrations of CO2 can be anticipated in the carrier gas, from wastewater to drinking water. Edinburgh Sensors’ Gascard® NG is a high performance OEM gas detector that provides real-time measurement of CO2 0-500ppm to 0- 3%.

OEM Gascard® NG

A suitable OEM solution for TOC monitoring, Gascard NG can be easily integrated into a range of gas detection solutions where lasting stability, high quality, superior repeatability and reliable measurement of carbon , CO2 and methane gas concentrations are needed. These features are due to Edinburgh Sensors’ proprietary dual wavelength fail to safe InfraRed (NDIR) sensor technology. The Gascard NG range offers ideal solutions for measuring and testing industrial as well as environmental gases. Table 1 shows the Gascard NG models for gas measurement range of CO2.

Table 1. Gas measurement range of CO2

Model* Gas measurement range CO2
Gascard NG 0 – 500 ppm**
Gascard NG 0 – 1000 ppm
Gascard NG 0 – 2000 ppm
Gascard NG 0 – 3000 ppm
Gascard NG 0 – 5000 ppm
Gascard NG 0 – 1%
Gascard NG 0 – 3%
Accuracy ± 2% of range ±<0.015% of range per mbar*
Zero stability ± 2% of range (over 12 months)*
Response time Bitswitch selectable T90 = 10 seconds or programmable RC
Operating temperature 0 – 45ºC
Operating pressure 800 – 1150mbar
Power requirements 24 V DC (7 – 30 V)
Warm-up time 1 minutes (initial) 30 minutes (full specification)
Humidity Measurements are unaffected by 0 – 95% relative humidity, non condensing
Output Linear 4 – 20 mA, 0 – 20 mA (bit switch selectable) maximum load dependant on supply voltage

* Not including calibration gas tolerance.
** Stability specification does not apply

The Gascard NG from Edinburgh Sensors comes with different interface options, such as true RS232 communication, analogue 4-20 mA/0-20 mA/0-5 v, serial interface for interfacing relay alarms and optional on board LANsupport. The on-board firmware is capable of supporting a modern graphical display or a conventional 4 segment LCD.

In addition, the Gascard NG series needs only minimum maintenance and thus eliminates significant amount of costs. Automatic pressure and temperature correction features allow real-time environmental condition measurements and thus provide consistent measurement and exact concentration readings of target gases.

The sensor head and electronics of the Gascard NG series are positioned on a Eurocard PCB with several bit-switches, which allow users to control different aspects of the sensors behaviour such as filter type and analogue output selection.

The Gascard NG is backward compatible with outputs from current generations of Gascard series and includes onboard true RS232 communications with the option of TCP/iP communications protocol and on-board data logging. With built-in features for multi-sensor and multigas operation, the Gascard NG can integrate additional gas detection technologies.

Features and Applications of Gascard NG Sensors

The key features of the Gascard NG OEM gas sensor (Figure 2) are as follows:

  • On-board barometric pressure correction in the range 800 - 1150mbar
  • New electronics platform with improved power and versatility of latest microprocessors
  • Wider operating voltage range (7V - 30V) and lower operating voltage (7V)
  • Extensive temperature compensation
  • True RS232 communications for data logging and control
  • Field replaceable IR source
  • Flexibility to integrate additional gas detection technologies
  • Optional on-board LAN support

Gascard NG OEM gas sensor

Figure 2. Gascard NG OEM gas sensor

The Gascard NG can be used in various applications such as waste water management, biogas, landfill, anaerobic digestion and sewage treatment.


Edinburgh Sensors offers an evaluation kit for OEM development. This kit includes a Gascard NG sensor, a relay board and a sophisticated graphical display interface that enables easy assessment of the Gascard NG functions.

In addition, Edinburgh Sensors’ engineers provide one-to-one customer service and technical support during the assessment and system integration process. The company is a major supplier of advanced gas sensor instruments that are made to deliver fast, precise and reliable measurements all the time.

This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.

For more information on this source, please visit Edinburgh Sensors.


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