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An automatically balancing isolation amplifier for the decoupling of measuring systems with high impedances

  • Instruments and Techniques
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Summary

It is theoretically shown that different conditions of coupling and grounding cause error voltages with the simultaneous use of two high-impedance measuring systems (e.g. pH electrodes). By the use of special amplifiers using optical transmission systems these error voltages are prevented. The transmission characteristics of the couplers are sensitive to changes in temperature due to the incorporation of infrared emitters in the system. An amplifying equipment with high d. c. stability was developed. The temperature drift was suppressed by the use of a special chopper stabilisation.

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Abbreviations

E E :

potential of the galvanic element glass electrode

E B :

potential of the galvanic element reference electrode

E G :

boundary liquid-wall of the reservoirs

f o :

switching frequency of the MOS FET-switches 300 Hz

j :

Gauss number (j 2=−1)

K 1 :

d. c. voltage gain of the amplifier (V 1): 36

K 2 :

d. c. voltage gain of the optical transmission system: 0.1

R b :

resistance of the reference electrode

R e :

resistance of the glass electrode

R EE :

input resistance of the amplifier (input glass electrode): 1012Ω

R EB :

(input reference electrode): 1012Ω

R 1–3,R K 1–4:

electrical resistances of the liquid between the electrodes and the wall of the reservoir

R G ,R G 1–2,T 1 :

time constant of the operational amplifier (V 1): 1.6 · 10−4 s

T 2 :

time constant of the optical transmission system: 3 · 10−6 s

T :

time constant of the hold elements: 0.1 · 10−6 s

(l):

radian frequency: s−1

u(t) :

time function of the voltage

U :

complex function of the voltage

References

  • Loeschcke, H. H., Sugioka, K.: pH of cerebrospinal fluid in the cisterna magna and on the surface of the choroid plexus of the 4th ventricle and its effect on ventilation in experimental disturbances of acid base balance. Transient and steady states. Pflügers Arch.312, 161–188 (1969)

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  • Opelt, W.: Kleines Handbuch technischer Regelvorgänge. 3. Aufl. Weinheim: Verlag Chemie 1960

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  • Süß, R.: Ein Ersatzschaltbild für die Glaselektroden-Meßkette. Arch. Techn. Messen (ATM)V 332–21, 89–92 (1960)

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Authors and Affiliations

  1. Institut für Physiologie, Ruhr-Universität Bochum, D-4630, Bochum, Federal Republic of Germany

    Klaus Mückenhoff & Alwin Luttmann

Authors
  1. Klaus Mückenhoff
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  2. Alwin Luttmann
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Mückenhoff, K., Luttmann, A. An automatically balancing isolation amplifier for the decoupling of measuring systems with high impedances. Pflugers Arch. 370, 93–97 (1977). https://doi.org/10.1007/BF00707952

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  • DOI: https://doi.org/10.1007/BF00707952

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