Biomedical Test Equipment By Polycarp Keraka, Western Technical College.

Defibrillator Analyzers

A Defibrillator Analyzer is basically meant to measure the energy content in the discharge pulse.It will analyze the pulse output of a monophasic or biphasic defibrillator. The primary measure of the output is the Energy that it contains. Other information deals with the maximum voltage and current as well as the pulses timing with respect to the R-wave. The human body has characteristic impedance may vary, but 50 ohms is used for comparative defibrillator testing. The Defibrillator analyzer has a large internal 50 ohm non-inductive resistor to simulate a body. It is sized to accept repeated pulses at the maximum energy levels.It works on the principle that the energy contained in a pulse of arbitrary shape and time is given by E== P dt P = V2 / R => E = V2 / R dt = V2 dt / R

This integral computation is implemented digitally by taking timed samples of the voltage every 100 μ seconds for 100 m seconds (1000 readings). Each value is then squared and divided by the resistance (50 ohms). The sum of these 1000 values times 10 is then the Energy in Joules (Watt Seconds) contained in the pulse. In other words, The defibrillating pulse is applied across a standard 50 ohm load and the voltage developed across it is given to a squaring circuit. The squaring circuit consists of four quadrant multiplier followed by an operational amplifier. The output of this device is a current which is proportional to the product of the two inputs. In the squaring mode, the two inputs are connected together so that the output is a square of the input voltage. The operational amplifier acts as a current to voltage converter, producing an output voltage which is proportional to the output current from the multiplier.

The defibrillator analyzer contains other circuits for controlling the measurement operations. For example, the pulse integrator circuit integrates the squared function pulse during the time that a pulse is present. During the remainder of the display time, it acts as an analog storage element. The voltage stored in the pulse integrator is read on the energy meter calibrated in watt-seconds.

Electrical Safety Analyzers

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