Gentec-EO T-Rad-USB (LEMO) - Manual (Page 11)

T-RAD-LEMO-USB Instruction Manual Version 1.0 June. 2012 11
Figure 8 Phase Specific Detector Output Signal
The multiplier action moves the signal to the frequencies at the sum and difference of the signal
and the reference frequency at 25Hz. Therefore the signal at 25Hz will move to 0Hz and 50Hz, as
seen. The 60Hz interference will move to 85Hz and -35Hz, not shown here. The odd harmonic of
the input signal at 75Hz moved to 100Hz and 50Hz, where it will add to the frequency shifted
signal. These signals can now be low pass filtered to extract the DC component.
3 Communications with Host PC
The T-Rad-USB communicates with the host PC via a USB port. The device supports full speed
USB 2.0. The implementation of the port in the host PC is accomplished via a Virtual Com Port,
or VCP. This in effect mimics a standard com port so that the user can take advantage of the
ease of developing custom applications with existing terminal emulators.
The Ports Settings are:
Baud Rate : 921600
Data Bits : 8
Stop Bits : 1
Parity : None
Flow Control : None
The host PC must have a terminal emulator as well as the T-Rad-USB USB drivers installed. These
drivers are installed by the disc supplied with the T-Rad-USB instrument.
4 Data Format
Measurement Data is sent from the T-Rad-USB as an Hexadecimal string.
The format is: DDDDCRLF
Where DDDD is a 12 bit value representing the ADC counts and terminated by a carriage return
followed by a line feed. The Lock in Amplifier algorithm is implemented in the Applications
Software.
5 Instrument Connections
The T-Rad-USB is connected to the host PC with a supplied USB cable. The instrument
communicates with the host PC via this cable, and the host PC supplies the power required by
the instrument.