Teardown of Servomex CO2 Analyzer 1400 Series

Old discarded equipment from a agriculture laboratory. Unfortunately damaged from the rough handling. This CO2 analyzer measures the CO2 levels in emissions using the principle of infrared absorption. It is used after a gas preparation system and set-points can be pre-defined and an alarm can be sounded if they are exceeded. A flow-rate alarm is also available. A 0 – 10 V analog output can be used to record the data on a plotter. Check out other teardown videos and articles from the agriculture laboratory here.

CO2 Analyzer hardware overview

The front and back of the unit shows that it from the user side is a fairly simply piece of equipment, while a lot more more is going on, on the inside. It is made by Servomex in England, Crowborough, Sussex. On the back there is mains input for 240VAC, a SK5 and PL5 connector for adjacent equipment and a gas in and outlet pipe. The front is fairly simple with a display, alarm LED and buttons. Adjustment of alarm or range is done by 4 potentiometers behind a small lid.

PCB of the display and controls shows a well layout design with high quality components.

The CPU of the unit is a Motorola MC6802p IC which runs at 1MHz with 128 bytes of RAM. The 4 MHz crystal next to the IC is used for the 6802 on-chip oscillator to produce the two-phase 1 MHz clock. The programs are located in the two custom Servomex ROMs dated back to 1990. The PCB features a lot of different components and ICs, that are perhaps chosen like that to hinder others from making a copy of the product. It is rare to see a CPU boards with so many different color components on.

The power supply seems to be four separate units. All controlled by a CA3524E/CA3130E/CA3140E switch mode power supply controller ICs. There is a high current supply for the analyzer chamber and another high power transformer for the infrared system. The rest is house keeping power supplies for the CPU and display.

With the lid off the unit, the first thing that comes in view is the analyzer chamber. With inputs on the right and a single signal output in a black cable on the left.

CO2 analyzer chamber

The detector and chamber construction is of very high quality. It incorporates two kind of detectors, possible one for reference and one that analyzes the gas through the flow chamber with the two pipe ports. The high current supply is for the infrared source. A port for air connection is blinded off. There is also a electromagnet to keep the rotating mirror in a brake position.

The PLT522 is a pyroelectric detector made of lithium tantalate. It has a compensation and amplifier circuit built into its round housing. The infrared filter coating on the rotating mirrors/filters is visible to be multiply layers seen through a microscope.

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