Isolation amplifier
Separation or isolation amplifier amplifier ( also English insulation Amplifier) are used to isolate smaller Spannungs-/Stromschwankungen that are modulated onto a circuit with voltage present. These must be an electrical isolation of the prestressed cable circuits of the amplifier circuits. This separation takes place in the simplest case of a double coil ( inductive principle transformer coupling ) or a capacitor ( capacitive coupling). This transmits only the voltage change / power fluctuations, but not the basic voltage.
Because of the " inertia " of the coil or the capacitor, the number of turns of the coil must ( technically correct inductor ) and a capacitor for coupling capacitance ( technically correct capacitance ) can be tuned to the frequency of the signal to be amplified. The characteristic of the coupling member, only certain frequencies pass ( band-pass filter ) is also the basis for a second effect of the buffer amplifier. Very short voltage peaks (about disorders as a result of Anschaltvorganges ) be disclosed only attenuated by the inductive coupling, and therefore weigh less sensitive amplifier components (diodes, transistors).
The above-mentioned frequency filter properties constitute a limitation, when a very broad range of frequencies to be amplified. This need is about in the field of audio electronics.
Because of the large bandwidth of transmitted frequencies, galvanic isolation is required, which has a low frequency selectivity. This can be done through the use of LEDs in combination with photo elements. A change in voltage produced here through the light-emitting diode a voltage change proportional to the size of the change in brightness. This is absorbed by the photovoltaic cell and amplifies the resulting photocurrent. This principle is called opto- electronic coupling.
Instrument isolating amplifier
With electronic subtractors can be - depending on the design - process voltages, which are superimposed with DC voltages between 10 V and 200 V. For the measurement of voltages, which are of high DC voltages superimposed ( in the kV range ), galvanically separated measuring amplifiers are needed. However, the galvanic isolation can also at lower voltages - for example for security reasons - done.
Here, the measuring circuit is divided into a transmitter and a receiver. The transmitter on the measuring potential, while the receiver is operating at a zero potential. For this purpose, a floating power supply is on the transmitter needs. The ground terminal of the floating power supply ( floating ground ) serves as a reference potential for the measurement of the transmitting part.
The power supply will be disconnected electrically, via a transformer. In addition, however, there is a capacitive coupling of a parasitic capacitance Cs. For this reason, high-frequency transformers are used here, which are (usually in the 100 kHz range ) operated with a high frequency sine wave oscillator. This very small coupling capacitances can be achieved with less than 10 pF.
However, if both measurement points are high impedance, even a very small coupling capacitance can lead to errors in the voltage floating ground connection. In this case, the potential difference is a Elektrometersubtrahierer, which is powered by the floating power supply is determined. This ensures that the test leads are de-energized. The floating ground is mounted as close as possible to the measurement object to hold the Gleichtaktaussteuerung the electrometer small.
In addition, the measured voltage needs to be electrically insulated transmitted to the receiver. To this end, the following types of galvanic isolation are used:
- The inductive coupling
- The capacitive coupling
- The opto- electronic coupling (optocoupler)
In inductive or capacitive coupling, the measured voltage to a substrate with a sufficiently high frequency to be modulated. Here, an amplitude, or pulse width modulation is used.
Using optocouplers, however DC voltages can also be transferred directly. The non-linearity of the optocoupler is suitable wiring - by comparison with an identical reference optocoupler - canceled.
Components
Isolation amplifier with inductive, capacitive and opto-electronic coupling are commercially available as finished components. Many types have this already built-in DC-DC converter. External DC-DC converters are therefore usually only used when operating with this multiple isolation amplifier with common floating ground.
Finished components that are require an external power supply is operated with an insulated power supply. These are available as ready devices such as the DCP02 series from Texas Instruments or the HPR100 series of C & D Technologies.
- Amplifier