Isolation amplifiers

The primary source of error is ground loop currents. This is caused by galvanic errors introduced by small potentials resulting from the ionic liquids and dissimilar metals that the electrode is in contact with in a bioreactor. Additional sources of error are interactions with other electrodes. We have frequently found that a pH electrode not connected to an isolation amplifier that floats the reference can show errors of 1-2 pH units. A simple test is to measure the pH of a buffered solution on-line and off-line to check the accuracy of a measurement. 

Fig. 14.1. Electronics for local tunneling spectroscopy. By using an op-amp with FET input stage as the isolation amplifier to the high-voltage amplifier for the z piezo, the holding time on the capacitor can be as long as 100 sec. The values of R and C show typical ranges.

Number of isolates from which a PCR product of expected size was amplified (300 bp) Number of isolates amplified solely by a single primer pair... 

Some SECM experiments require an isolation amplifier to avoid electrical interference. One example occurs with a potentiometric tip and a potentio-static electrode, such as a pH-sensitive tip at a polarized corrosion test sam-... 

Guthold, M., Cubicciotti, R., Superfine, R., Taylor, R. M. (2002). Novel methodology to detect, isolate, amplify and characterize single aptamer molecules with desirable target-binding properties. Biophys J. Supplement, Abstract, 163C. 

We have used the coUagen-glycosaminoglycan (coUagen-GAG) mesh scaffold to probe molecular level cell-biomaterials interactions [11]. We seeded IMR-90 human fibroblasts onto three-dimensional (3-D) collagen-GAG meshes and control surfaces of tissue culture polystyrene (TCPS). Nucleic acids (mRNA) from cells from each culture were isolated, amplified, and hybridized to human genome microarrays (U133A Gene Chip, Affymetrix, Santa Clara, CA). 

Introduction Basic Amplifier Requirements Isolation Amplifier and Patient Safety Surge Protection Input Guarding Dynamic Range and Recovery Digital Electronics Summary Defining Terms References Further Information... 

Isolation amplifiers can be used to break ground loops, eliminate source ground connections, and provide isolation protection to the patient and electronic equipment. In a biopotential amplifier, the main purpose of the isolation amplifier is the protection of the patient by eliminating the hazard of electric shock resulting from the interaction among patient, amplifier, and other electric devices in the patient s environment, specifically defibrillators and electrosurgical equipment. It also adds to the prevention of line frequency interferences. 

Transformer-coupled isolation amplifiers perform on the basis of inductive transmission of a carrier signal that is amplitude modulated by the biosignal. A synchronous demodulator on the output port reconstructs the signal before it is fed through a Bessel response low-pass filter to an output buffer. A power transformer, generally driven by a 400-900 kHz square wave, supphes isolated power to the amplifier. 

FIGURE 9.7 Equivalent circuit of an isolation amplifier. The differential amplifier on the left transmits the signal through the isolation barrier by a transformer, capacitor, or an optocoupler. 

FIGURE 9.11 Passive isolation amplifier can be operated without the need for an isolated power supply (a). The biological source provides the power to modulate the load impedance of an inductive transformer. As an easy realization shown in (b), an FET can be directly connected to two electrodes. The source-drain resistance changes as a linear function of the biopotential that is then reflected by the input impedance of the transformer. 

This two-lead isolation amplifier design is not limited to telemetric applications, it can also be used in all other applications where its main advantage lies in its simplicity and the resulting substantial cost savings as compared to other isolation amplifiers that require additional amplifier stages and an additional isolated power supply. 

Isolation mode rejection ratio (IMRR) IMRR of an isolation amplifier is defined as the ratio between the isolation voltage, V,so. and the amplitude of the isolation signal appearing at the output of the isolation amplifier or as isolation voltage divided by output voltage in the absence of... 

Figure 6.30 also shows that a Hall effect transducer and a voltage isolation amplifier are used in the system, which provides independent measurement of the pulsed current and voltage drop between the two rams, respectively. The RMS values of the electrical variables are important for the correct evaluation of the Joule heat distribution, which is demonstrated by the comprehensive analysis of the system behavior from the electromagnetic perspective. With these instantaneous measurement results, the corresponding average values of various parameters can be calculated as [42] ... 

An isolated amplifier is referenced only to the body under measurement and so in principle does... 

In addition to an improvement in electrical safety, isolated amplifiers in principle should eliminate line-frequency noise in biopotential recordings in the same way as does biotelemetry. The biopo-... 

FIGURE 17 J6 Photograph of a commercial isolation amplifier module. 

---