VXI VT1422A - Manual (Page 45)

Field Wiring 45 Chapter 2
Terminal Module
Considerations for
TC Measurements
The isothermal characteristics of the VT1422A Terminal Module are crucial for
good TC readings and can be affected by any of the following factors:
1. The clear plastic cover must be on the Terminal Module.
2. The thin white mylar thermal barrier must be inserted over the Terminal
Module connector. This prevents airflow from the VT1422A A/D Module
into the Terminal Module.
3. The Terminal Module must also be in a fairly stable temperature environment
and it is best to minimize the temperature gradient between the VT1422A
module and the Terminal Module.
4. The VXI mainframe cooling fan filters must be clean and there should be as
much clear space in front of the fan intakes as possible.
5. Recirculating warm air inside a closed rack cabinet can cause a problem if
the Terminal Module is suspended into ambient air that is significantly
warmer or cooler. If the mainframe recess is mounted in a rack with both
front and rear doors, closing both doors helps keep the entire VT1422A at a
uniform temperature. If there is no front door, try opening the back door.
6. VXI Technology recommends that the cooling fan switch on the back of the
of the CT-400 Mainframe be in the "High" position. The normal variable
speed cooling fan control can make the internal VT1422A module
temperature cycle up and down, which affects the amplifiers with these
microvolt-level signals.