Lockin

Figure 9.8. A total power radiometer with an AC-biased bolometer feeding an audio amplifier followed by a lockin amphfier. This design is used in BOOMERanG and will be used in the Planck HFI.

Figure 9.9. A differential radiometer with an optical chopper so the bolometer looks alternately at two sky different sky positions. The bolometer feeds an audio amplifier followed by a lockin amplifier.

Figure 9.13. A correlation radiometer with a phase switch inserted in both arms. One of the phase switchs is driven to modulate the output of the multiplier so a lockin amplifier can be used.

The 1// gain fluctuations in HEMTs require a high chopping frequency. Prior to the lockin amplifier, the variance of the output of a HEMT radiometer in a 1 Hz bandwidth (tint = 0.5 sec) centered at / is given by... 

This is 0.04 Hz for the worst case WMAP radiometer, W4, which has both the highest bandwidth and the highest offset. Ideally the post-lockin 1// knee... 

In a PA experiment, the excited-state absorption spectrum is measured. The sample was excited by an amplitude- modulated pump beam and changes in the transmission of a probe beam are measured by lockin amplification of a photoreceiver. The 363-nm line of an argon ion laser at a power density of 30 mW/cm2 was used as the pump beam and a monochromated tungsten white-light source was used as the probe. The pump beam was modulated at 120 Hz by an acousto-optical modulator and the spectra were measured under... 

Design for controiiabiiity Barriers Lockouts Lockins Interlocks... 

Isolation, lockouts, lockins, and interlocks are some of the most commonly used safety measures in the process industry. These controls are constructed on three basic principles, or else on combinations of the first two. The three principles are ... 

Locking a switch on a live circuit to prevent current fiom being shut off is a lockin. 

A lockin is a protective device that restricts personnel inside specific limits to prevent contact with a hazard outside those limits or that maintains the hazard inside those limits so that it cannot affect anything outside. 

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