Instrumentation amplifier repeatability

However the probe, like the bath, does suffer from the same difficulty with respect to temperature control. This problem has been alleviated to some extent in modern instruments by the incorporation of a pulse mode of operation. Quite simply this consists of a timer attached to the amplifier which switches the power to the probe on and off repeatedly. The off time allows the system to cool between the pulses of sonication. The on time is represented as a fraction of the total time involved in the cycle (about 1 s) i. e. 100 % is continuous sonication while 50 % represents 0.5 s bursts of power every 0.5 s. 

The basic operation of the instrument (3) consists of the Ionization of the sample in the cell by a timed electron beam which Is followed, after a short Interval, by an RF pulse applied to the plates of the cell. This pulse coherently excites all ions In the cell into cyclotron motion. The motion continues after cessation of the pulse, and the resonance is detected by the plates of the cell, amplified and the data stored In the computer. The excltatlon/detection cycle is repeated numerous times and the collected data summed. The data Is then subjected to fourler transformation and the frequency spectrum resulting converted into a mass spectrum. The spectrum Is normalized to the major peak. For quantitative work, the calibration can be based either on peak height or peak area. Here, major considerations will Include the resolution chosen and the relative concentrations of the constituents under Investigation. 

For the ISI of small diameter and thick ICr-lMo (ferromagnet material), RFECT is an efficient technique. For this, a state-of-the art instrument has been devdoped. This RFECT instrument essentially consists of a low frequency osdllator, a lock-in-amplifier and allied circuitry. Spedal V-notch filters have been used to suppress the interferences from line frequendes and signal optimisation is achieved with the use of high-pass and low-pass filters. The instrument has demonstrated, repeatable and unambiguous detection of wall loss down to 10% wall thickness in 9Cr-lMo sted tubes. 

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