Gentec-EO T-Rad-USB User Manual

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WARRANTY

First Year Warranty

The Gentec-EO thermal power and energy detectors carry a one-year warranty (from date of shipment)
against material and /or workmanship defects when used under normal operating conditions. The
warranty does not cover recalibration or damages related to misuse.

Gentec-EO will repair or replace at its option any wattmeter or joulemeter which proves to be defective
during the warranty period, except in the case of product misuse.

Any unauthorized alteration or repair of the product is also not covered by the warranty.
The manufacturer is not liable for consequential damages of any kind.
In the case of a malfunction, contact the local Gentec-EO distributor or nearest Gentec-EO office to obtain

a return authorization number. Return the material to the address below.

All customers:

Gentec-EO, Inc.
445 St-Jean-Baptiste, Suite 160
Quebec, QC, G2E 5N7
Canada

Tel: [phone]
Fax: [phone]
Email: [e-mail]
Web: www.gentec-eo.com

Lifetime Warranty

Gentec-EO will warranty any thermal power and energy detector head for its lifetime as long as it has
been returned for recalibration annually from the date of shipment. This warranty includes parts and labor
for all routine repairs including normal wear under normal operating conditions.

Gentec-EO will inspect and repair the detector during the annual recalibration. Exceptions to repair at
other times will be at Gentec-EO’s option.

Not included is the cost of annual recalibration or consequential damages from using the detector.
The only condition is that the detector head must not have been subject to unauthorized service or

damaged by misuse. Misuse would include, but is not limited to; laser exposure outside Gentec-EO’s
published specifications, physical damage due to improper handling, and exposure to hostile
environments. Hostile environments would include, but are not limited to excessive temperature,
vibration, humidity (>80%), or surface contaminants; exposure to flame, solvents or water; and connection
to improper electrical voltage.

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TABLE OF CONTENTS

WARRANTY........................................................................................................2

TABLE OF CONTENTS ......................................................................................3

LIST OF ILLUSTRATIONS .................................................................................4

1 GENERAL INFORMATION 5

1.1 . System Overview 5

2 Lock In Amplifier Theory of Operation 5

2.1 . Mathematical Description of a Lock In Amplifier. 5

2.2 . Time Domain Description of a Lock In Amplifier. 7

2.3 . Frequency Domain Description of a Lock In Amplifier. 10

3 Communications with Host PC 11
4 Data Format 11
5 Instrument Connections 11
6 Using the Instrument 12
7 Using the Applications Software 13

7.1 . The Main Display Panel 13

7.2 . The Strip Chart Display 16

7.3 . The Tuning Needles Display 18

7.4 . The Setup Display 20

7.5 . The Display Menu 23

7.6 . View Wavelength Correction Table 23

7.7 . The Help Menu 24

8 DECLARATION OF CONFORMITY 25

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LIST OF ILLUSTRATIONS

Fig. 1 Input signal ....................................................................................................................... 7

Fig. 2 Reference signal .............................................................................................................. 8

Fig. 3 Result of multiplication ................................................................................................... 8

Fig. 4 Output with 100ms time constant .................................................................................. 9

Fig. 5 Output with 1s time constant ......................................................................................... 9

Fig.6 Corrupted Input Signal .................................................................................................. 10

Fig. 7 Band Pass Filtered Corrupted Input Signal ................................................................ 10

Fig.8 Phase Specific Detector Output Signal ....................................................................... 11

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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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If we set B to unity and hold it constant, then the result is a signal that is:

1. Proportional to the A, the amplitude of the input signal.

2. Proportional to the cosine of the phase angle between the two signals.

3. Modulated at two times the input signal frequency.
If we set the phase difference to zero degrees then the resulting signal can be passed through a

low pass filter with a time constant of tau and the result will be:

This shows that once the filter has settled, the signal is a DC representation of the original input. We can
now set the filter time constant as high as needed to block out unwanted noise and interference. The
details of how the lock in implements this math can be found in the literature.

One subject of interest arises from the requirement to set the phase difference to zero degrees. In
practice, the phase difference is not known. Since the cosine function returns values between one and
negative one as the phase is changed, the phase is simply adjusted until the signal maximizes. It is
actually easier to adjust the phase until the signal goes to zero and then shift the phase by 90 degrees. If
the signal goes negative, shift the phase 180 degrees. The signal will now be maximized.

If this seems like a bother, it is. The Gentec-EO Lock In Amplifier uses a dual phase approach which
relieves the user of the need to adjust the phase. A sine wave signal is generated by the instrument at the
reference frequency, and at the reference frequency plus 90 degrees, or pi divided by 2. The input signal
is multiplied by both reference signals. The results of those multiplications are then squared, summed,
and the square root is taken. Look at the final equation for the output after the multiplication, ignoring the
second term:

The output of the second multiplication will be:

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If we square these and add them together we obtain:

Now taking the square root gives:

The output of the multiplication is no longer phase dependant.

2.2 Time Domain Description of a Lock In Amplifier.

The input signal has peak amplitude of 5V (10V peak to peak) and a frequency of 25Hz and is
shown in figure 1.

Figure 1 Input Signal

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The reference signal supplied by the lock in signal has peak amplitude of 1V and a frequency of
25Hz and is shown in figure 2.

Figure 2 Reference Signal

After multiplying the two signals using a circuit called a Phase Specific Detector in ananalog lock in, or by
direct math in a digital lock in, the output signal is shown in figure3. Note that its peak to peak amplitude is
5V, or ½ of the input and its frequency is 50Hz,or twice the input frequency. Also note it now has a DC
offset of the peak voltage of the input signal divided by 2 as predicted. This DC offset is what the low pass
filter will pull from figure 3.

Figure 3 Result of Multiplication

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