VTA
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16 VTA
16.1 Introduction
VTA is the abbreviation for Variable Temperature System Adapter.
For application specific needs a wide variety of temperature sensors and heater interfaces
must be supported. Some NMR probes need standard thermocouple sensors type-T, others
need PT100 thermistors, some need two sensors etc.
To obtain precise and accurate temperature measurement the analog sensor signal cannot
be carried over long distances or have many connector contacts between sensor and
electronics.
Many NMR users want to work with different NMR probes and therefore must change the
sensor adaptation conveniently.
For every temperature sensor and heater adaptation variant or other accessory device a
tailored VTA is available but only one type of cable connection is needed for probe to console
adaptation. This cable carries wires for digital signals, low-voltage power supply and the
heater power.
The VT Adapters for probe head temperature control:
• Adapt the specific sensor, convert the sensor signal to a digital temperature reading and
transmit this value to the BSMS/2 ELCB.
• Measure the environmental temperature, use this value to compensate the room
temperature dependencies of the specific sensor and transmit the room temperature value
to the BSMS for further elimination of room temperature artefacts.
Heater power and heater safety sensor signals are fed through the VTA for three reasons:
• The heater power and the corresponding regulation sensor are bundled, thus preventing
erroneous usage of a spare sensor for regulation.
• The heater over-temperature sensor can be evaluated.
• The heater current can be filtered close to the probe, suppressing RF noise picked up by
the long cable running from the console to the magnet.
To connect other temperature accessories like chillers, heat exchangers, nitrogen level
measurement, pressure measurement etc. there are dedicated VTAs available. These
accessory adapters are connected through a thinner cable that carries digital signals and low-
voltage power supply only.
16.2 Configurations
The various applications and related VTA variants are presented in the following chapters:
• BSVT Probe Adaptation [}126]
• BSVT and HT Solids Probe (High Temperature) [}132]
• BSVT and VT Gas Cooling Accessory Adaptation [}134]
• BSVT and Flow Probe Adaptation (FLOW-NMR) [}138]
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