Gentec-eo T-Rad-USB (LEMO) Manuel d'utilisateur télécharger pdf (Page 5)

T-RAD-LEMO-USB Instruction Manual Version 1.0 June. 2012

1 GENERAL INFORMATION

1.1 System Overview

Welcome to the T-Rad-USB Application Software. This software, when coupled with a Gentec-EO

T-Rad-USB, provides the user with a versatile measurement system. There are multiple sensors

available for the system. When a sensor is mated to the USB module, the module reads the

sensor type, sensor calibration, sensor wavelength response, and configures the hardware

appropriately. When the Application software is started it queries the T-Rad-USB and configures

itself for the appropriate measurement system. For this reason the application software will not

always show all control and indicators, i.e., it will not have Trigger controls and indicators for an

Optical Power Meter.

The Applications Software communicates with the host PC via a USB port. The system uses the

T-Rad-USB Command Set to do this.

Data is sent to the host PC when the instrument has had its data gate turned on. The sampled

data is sent to the application at 1 kHz. The Lock In algorithm is implemented in the application.

2 Lock In Amplifier Theory of Operation

The operation of a Lock In Amplifier can seem mysterious given its ability to pull a useful signal

out of noise and interference, but the basics of operation are not complex. A lock in amplifier's

operation can be explained in three ways: mathematically, in the time domain, or in the frequency

domain. While all explanations are equally useful, the one that makes sense to the user is the

most useful, so a brief description of all three will be presented.

2.1 Mathematical Description of a Lock In Amplifier.

Fourier Theory tells us that all repetitive signals can be broken down into a series of sine’s and

cosines. Because of this fact, we can describe the lock in operation using a signal that is a pure

cosine wave. To go further, even if the input signal is not a pure cosine wave, the lock will extract

the pure cosine wave component of the signal anyway, so the approach is justified. Consider an

input signal, v (t), given by:

Now consider a second signal, the reference signal, given by:

This reference signal is at the same frequency as the input signal and is supplied by thelock in.

If we multiply the two signals, we get

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Gentec-eo T-Rad-USB (LEMO) Manuel d'utilisateur Page 5