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CHAPTER 2:
Magnet System Design, Installation, and Operation
Model 648 Electromagnet Power Supply
2.4.3 Temperature
Switches and Flow
Switches
As discussed in section 2.4.1, water-cooling for the magnet is essential. To protect the
magnet from damage resulting from an interruption in cooling water, a flow switch,
temperature switches, or both should be installed. The switches must have a
normally open contact (switch is open when no water is flowing), and if switches are
used, they must be connected in series. The switches are then connected to the flow
switch terminals of the magnet connector on the Model 648. The Model 648
monitors the switches and if an open is detected, the output current is ramped to
zero. (Flow switch monitoring depends on water valve mode setting. See section 4.13
and section 4.14 for details.) Given the cost of the magnet, it is prudent to use both
temperature and flow switches. Some installations use two flow switches, one in the
exhaust line of each coil so that if a clog occurs in only one coil, it can be detected.
FIGURE 2-4 shows the typical flow and temperature switch connection.
Care must be used in the selection of the flow switch. Some switches use a sensitive reed
switch, which can be overpowered by stray flux from the magnet and will not open when
the magnet is operating at high field. The flow switch must be tested by turning off the
water while the magnet is operating at full current.
Typical thermal switch, flow switch and valve wiring
To Model 648 magnet connector valve contacts
To Model 648 magnet connector flow switch contacts
Inlet
Outlet
Thermal switch
Flow switch
Water valve
Thermal switch
2.4.4 Cooling Water
and Water Valve
The cooling water for the magnet can be drawn from the municipal water facility or
from a dedicated re-circulating water chiller designed for this purpose. When water is
drawn from the municipal water facility, the water should be turned on only when it
is required to reduce consumption and reduce the likelihood of scale build-up and
condensation in the magnet. The water can be turned on and off manually when the
magnet is used, or automatically with a solenoid valve. The Model 648 provides
automatic control and a 24 VAC at 1 A output for this purpose. The optional water
valve is shown in FIGURE 2-2. The water inlet line should also be fitted with a
sediment filter (not shown) to reduce scale build-up in the magnet coils and
connecting lines.
FIGURE 2-4
