Questions and answers about LGD Compact
FAQ LGD Compact
- Emission monitoring (CH4, NH3), vehicle based, portable and fix installations for:
- Landfills (including flare-off) and sewer monitoring
- Greenhouse gas emission monitoring (GHG)
- Research for under water emissions and climate changes
- CH4 / city gas network leak search: vehicle-based or portable
- CH4, CO2 and NH3 for gas detection in medical breath analysis
- CH4 and NH3 monitoring in livestock operations: climate control and scrubber monitoring (metrology suitcase, stream-switched systems)
- NH3 and H2O in biogas and natural gas quality control
- CO2 in amine scrubbing and process control
Each LGD Compact module is designed to measure one particular gas since the tuning range of a laser diode is limited to a few nanometers. However, it is sometimes possible to measure two gases with the same laser if the absorption lines are closely interlaced (e.g. water and ammonia or methane and carbon dioxide). The feasibility of measuring two gases also depends on the gas matrix. For further details on specific applications, the technical support team will be happy to assist you.
The LGD Compact is designed as a self-contained and stand-alone device. Only a power supply needs to be provided and, in case of the non EMC-conform version, take care about the proper shielding of cables and electronic boards (recommendations for shielding can be found in the LGD Compact Operating Instructions). Thanks to low power consumption the LGD Compact is also suitable for battery operation. A Technical Note for battery recommendations is available on request. Conditioned gas needs to be supplied to the module, this means filtering for dust and avoiding condensation in the measurement cell is required. Suitable filters depend very much on the application and should be selected with the help of a filter manufacturer. The temperature of the incoming gas has to be adapted to the cell temperature as close as possible. Thanks to its small size and light weight design the LGD Compact can be integrated in small and portable housings and vehicles (like a drone for example). Most applications may contain other analytical elements such as a pump, filtration elements and a power supply. A gas pump can be installed either upstream or downstream of the LGD Compact, but the resulting positive or negative pressure in the LGD Compact should be between 800 and 1100 mbar, respectively.
To operate the LGD Compact in mobile applications powered by a battery, it is recommended to select a battery voltage between 3.7 and 5 V. Ideally, this battery should guarantee a power consumption of 1W over a period of up to 10 hours. More detailed information and recommendations on the different battery types are available on request in a Technical Note.
The LGD compact module will be delivered with an electrical cable from sensor housing to electronic boards and EMC conformity will only be granted for product executions with shielded cable versions together with electronic box.
If this shielded cable (straight or angled version) cannot be used due to integration issues the cable packaging should follow at least these recommendations:
- Conductor cross section 17x 0.14 mm² (signal line), AWG 26
- Fully shielded cable with good shield connection
- Max. cable length = 350mm (in general as short as possible)
The diagrams for cable wiring can be seen in the Operating and Integrating Instructions in Chapter 3 – Instructions for LGD system integration.
1.6 What is the best practice for mounting the LGD Compact?
As the LGD Compact has an opto-mechanical adjustment it’s important to avoid big mechanical vibrations or mechanical shock that could lead to system misalignment and performance degradation. The LGD Compact has two M4 threaded holes on the side for mounting. For environments where important vibrations can’t be avoided, dampers could be mounted on the LGD Compact to attenuate the mechanical vibrations.
The LGD Compact has successfully passed the shock testing regarding EN60068-2-27:2009 with max acceleration 150 m/s2, 11 ms, half sinus, 18 cycles and the vibration testing regarding EN60068-2-6:2008 5 - 55 Hz, amplitude 0.35 mm, 1 octave/min, 2h 20 min per orientation (20 frequency cycles).
The best performance can be achieved when the module temperature is stable, i.e. not exposed to ambient temperature changes.
When ambient temperature changes occur (e.g. during the warm-up time or when turning on the room’s air conditioning), the performance of the instrument is governed by the “Accuracy” value as given in the product data sheet. (Also, see the target analogy graph in here). When the temperature of the instrument is stable and as well as the temperature around the instrument, the performance is governed by the “Precision” value in the specifications. This “short-term noise” can be improved by averaging measurements over a certain period of time (e.g. 5,10 or 30 s). Generally Precision improves with the square root of the number of measured. E.g. a 10s average results in 3.3 times better precision.
If a small amount of moisture has condensed on the cell windows in the LGD Compact, it can be eliminated in most cases by flushing with dry air or nitrogen. However, once the gas cell has been "flooded" or the condensate has dried on the mirrors, a repair will almost certainly have to be made. The performance of the LGD Compact can be verified by the "Power on Photodiode" value in the "Diagnostic Data". If the value is still greater than 0.8 no significant performance losses are to be expected. Only if the value is less than 0.5 a service will soon be necessary. It’s not recommended to open the device to try to clean the cell and cell windows that will on one hand void the warranty (warranty stickers) and on the other hand degrade the performances of the LGD modules. Only operators trained by Axetris can proceed to internal cleaning and repair as this needs special knowledge and special equipment to verify performances after the repair is performed.
The recommended flow rate for the LGD Compact is between 100 - 3000 ml/min. However, lower or higher flow rates can also be applied, this only affects the T90 reaction time. Care should always be taken to ensure that the operating pressure of 800 to 1100 mbar is respected.