How to build an oxygen or temperature analyzer with analog output and regulator function:
Back in the 1970'ies researchers at Department of Zoophysiology, University of Aarhus, Denmark initiated a series of experiments concerning the adaptation of fish to hypoxia. For long term exposure to preset levels of hypoxia an instrument or regulator was developed by engineer Einer Larsen. The analog output from a Radiometer PHM71 acid-base-analyzer, connected to a Radiometer pO2 electrode located in the fish tank, drove a specially designed oxygen regulator that opened or closed a solenoid valve connected to a compressed nitrogen cylinder connected to air stones in the tank (Wood et al., 1975). For years this system was used in several laboratories world wide.
The instrument:
Nowadays however, there is no reason to make your own circuit board because the commercial Programmable LED indicator PR 5714 from PR Electronics has most of it build in. It can be used either directly with a galvanic oxygen probe or with the analog voltage output signal from any oxygen meter with this option (WTW, Presens, Orion, YSI etc). It has 2 relays for solenoid valves, pumps or alarms as well as an analog recorder output. It will run on any voltage from 24 to 230 Volt AC or DC. In addition it is front key programmable. The instrument alone is about € 200,-
Beside the PR 5714 you only need a few components:
1: For the oxygen electrode you need to mount a resistor across pin 41 and pin 44. This should bed done in the plug of the probe since you then quickly can change the instrument to become a temperature monitor and regulator.
2: You need to mount a self releasing push-bottom or switch between pin 41 and 44. This allow you to zero calibrate the oxygen input signal.
3: If you would like to use the analog output option you should mount a 250 Ohm resistor across pin 11 and pin 12. The signal is default the industry standard of 0 - 20 or 4 - 20 mA, but when you add the resistor it is converted to 0 - 5 or 1 - 5 Volt. A 250 Ohm resistor is hard to find but just use a 249 Ohm resistor instead.
4: In addition you need a few plugs for oxygen signal input, instrument analog output, a plug for an instrument power cable, and up to two plugs for the regulator output to the solenoid valve(s).
5 : Finally if you want to regulate oxygen tension in the water you need a solenoid valve. I use valves from Martonair as well as from Burkert. They can be either 24, 110 or 230 Volts.
Manual for Oxygen Monitor:
In Progress! Or find the manual for a commercial nearly identical oxygen regulator. Only nearly identical, because the one described here can be used as an oxygen analyzer/regulator as well as temperature analyzer/regulator. The comercial model can't because they want to sell you two different instruments.
Galvanic oxygen electrodes that can be used with the regulator:
All galvanic oxygen electrodes from Oxyguard International can be used. They all cost approximately € 400,- each. The most appropriate models are:
2: Oxygen Mini
Conclusion:
For a few hundred Euros you can build your own oxygen or temperature monitor with analog output and regulator function.
Temperature Monitor:
If you want to be able to measure and control temperature you should purchase a Pt100 4-wire sensor. I have good experience with Ametek resistance temperature cable sensor with silicone cable (Spec. no. 1710-xxx). Cost approximately € 75,-
To control the temperature of an experimental aquarium you obviously don't use a solenoid valve as above, but can use a small aquarium pump to recirculate water between the experimental tank and a coil in a colder or warmer water bath, depending on if you want a higher or lower temperature than the ambient.
Manual for Temperature Monitor:
In Progress! Or find the manual for the commercial model on the web.
References:
Wood, S. C., Johansen, K. & Weber, R. E. Effects of ambient PO2 on hemoglobin-oxygen affinity and red cell ATP concentration in a benthic fish. Respiration Physiology. 1975; 25; 259-267.
Last updated January 2015
