User`s manual

Lake Shore MTD Series Cryotest System User’s Manual
3-2 Installation
Environmental Requirements (Continued)
It is imperative that adequate ventilation of work area be provided. This will prevent build up of
potentially life-threatening concentrations of helium and nitrogen gas. Refer to Appendix E for further
information. Oxygen content monitor/alarms should be installed near the work site to warn against low
oxygen levels. The air-conditioning system should provide filtering to reduce dust and other particulate
matter to a reasonable level. If salt air, corrosive gases, or other air pollutants are present, special
filtering arrangements may be required and an air-conditioning expert should be consulted.
3.2 SYSTEM POWER AND GROUND REQUIREMENTS
The AC power source for components associated with the MTD System must be frequency and voltage
regulated and isolated from sources that may generate Electromagnetic Interference (EMI). The MTD
exhaust gas heater is designed for single-phase 3-wire alternating current (AC) power. Two-wire
(without ground) AC power must not be used. Ground Fault Interrupter (GFI) and Transient Surge
Protection circuitry at the AC source is also strongly recommended.
In areas where the AC voltage is variable, the Customer should consider the use of a constant voltage
transformer. If power outages are a problem, an Uninterruptable Power Supply (UPS) should also be
considered.
CAUTION: Do not attempt to apply electrical power to the MTD System until all instruments have
been checked for proper input power settings and fuse or circuit breaker ratings.
To protect operating personnel, the National Electrical Manufacturer's Association (NEMA)
recommends, and the National Electrical Safety Code requires, instrument panels and cabinets be
grounded. The safety ground has two functions: (1) to provide a true ground path for electrical circuitry,
and (2) in the event of internal electrical faults, such as shorts, to carry the entire fault current to ground,
thus protecting operating personnel from hazardous shock. This instrument is equipped with a
detachable three-prong power cable which powers the exhaust gas heater that, when plugged into a
3-wire receptacle, grounds equipment in the Instrument Console.
EMI is an electromagnetic phenomena which, either directly or indirectly, can contribute to a degradation
in performance of an electronic system. EMI can be both natural and man-made. Natural sources of
EMI include thunderstorms, solar disturbances, cosmic rays, etc. Man-made sources of EMI include
fixed and mobile transmitters, high voltage power lines, power tools and appliances, florescent lights,
and other equipment containing motors, heaters, etc. Ensure that the AC source is well protected from
these types of EMI. Transient surge protectors should be considered for lightning protection.
3.3 PHYSICAL SUPPORT REQUIREMENTS
It is important to stabilize the MTD to prevent the system from tipping over or falling. The preferred
method is the use of the optional Model 1705 Horizontal Cradle Mount Assembly. An alternative method
is to clamp the MTD Handle/Ring Stand Assembly to a table surface.
NOTE: If the MTD System is rotated more than 90° off the vertical position (e.g., with the
handle/ring stand down), the liquid helium flow rate will have to be increased.
3.4 LIQUID CRYOGEN
The Model MTD-150 Cryostat can be operated with either liquid helium or liquid nitrogen. This manual
assumes operation with liquid helium. The operating procedure for liquid nitrogen is essentially identical
except for control valve settings. The MTD-150 system is designed to avoid problems associated with
the high latent heat of liquid nitrogen when operating in a variable temperature mode (77
– 400 K).
3.5 STORAGE DEWAR PRESSURIZING
A cylinder of welding grade helium gas is suitable to pressurize the storage dewar whether it is filled
with liquid helium or liquid nitrogen. A pressure regulator and gauge with a range of 0
– 10 psig is
recommended. A vapor port on the storage dewar neck allows for the pressurization connection.
Storage dewars not equipped with a pressurization provision can use an adapter tube and pressure hat.