Valco baby Vici TCD-3, Инструкция по эксплуатации

Страница: 6 / 42

2
Introduction
Operational Overview
System parameters such as detector cell temperature, filament power levels,
output channel nominal voltage levels, and communication settings must be
entered through the serial communications port. This can be done either with
the included Graphical User Interface (GUI) or by entering direct commands with
a terminal emulator program.
New parameters entered into the TCD-3 are saved in non-volatile memory,
becoming the values referenced the next time the controller is turned on.
Once parameters are stored, the TCD-3 may be operated without a serial port
connection, unless testing criteria change and new parameters must be entered.
By default, these stored settings are implemented immediately when the con-
troller is turned on. However, this default behavior can be altered through serial
port commands. A start-up delay may be added, allowing other system compo-
nents to initialize before the TCD-3 is enabled. Or, the TCD-3 may be configured
to power-up in an idle mode, in which no power is applied to the detector heat-
ing elements until a serial command is received.
Refer to “Appendix B: Basic TCD
Operation via Serial Commands” on page 32 for further details on these options.
Once the TCD-3 is enabled, the controller applies power to the detector heaters
until the detector reaches its target temperature setting. The TCD-3 then
monitors the temperature until it is within the minimum accuracy setting for
30 minutes, at which point the system is reported as stable. System stability is
indicated via the controller’s front panel status LED, the READY digital output
signal (available on the rear on the unit), and through the RS-232 communication
port.
After the detector has reached thermal stability (with constant carrier gas flow),
the filament channels of the detector achieve a low-drift, low-noise operational
state. Measurements of the energy states of the detector filaments are avail-
able from the controller’s three analog output channels. Output Channels A
and B reflect the energy state of filaments A and B, respectively. The third analog
output, Channel AB, is a referenced output derived from the difference of the two
filament energy states (
i.e., Channel A – Channel B).
Each of these analog signals has a very narrow bandwidth, and is generated as
an offset from a reference voltage. The level of this reference voltage varies, as it
is dependent upon system temperature, filament power, environment, carrier gas,
etc. Because of this variance, the output channels must occasionally be adjusted
so that their signals are within the output limits of the unit. This adjustment
process, which tunes the reference voltage until the differential output signal
level matches the desired voltage, is often referred to as “zeroing” (although the
process can actually be used to adjust the output levels to values other than 0 V).
The zeroing routine should be initiated before each chromatographic test to
correct for any signal drift between tests. The routine should not be executed
until the detector temperature has had adequate time to settle and stabilize. If
the signal is currently out of range, the routine may take up to 10 seconds to
complete. However, once the channel is within the control band, the adjustment
routine should complete within 2 seconds.
Once the TCD-3 system has been properly plumbed, the detector has reached
thermal stability, and the output channels have been “zeroed”, the TCD-3 system
is ready for use.