Termaline® Load Resistor
3
Cooling Water for Models 8792
The electrical performance of these RF loads is affected by impurities or other chemical additives in the cooling
water. The presence of salts in the water definitely makes the device unusable because salts cause a rapid increase
in VSWR. Therefore sea water or silty water should not be used for cooling the loads,
The thermal performance of these loads is also affected by impurities, particularly those impurities that accumulate
in the form of scale on the exposed surfaces of the coolant paths of the load assembly. These deposits may result in
an increase in the thermal and/or fluid resistance(s) of the load and may in turn cause the load to overheat and fail.
The following types of water are considered safe for the cooling of the Models 8792 Load Resistor: filtered, city, or
soft water. In general, any potable water is suitable for cooling the load.
Flow Interlock Control Circuit (Optional)
The interlock control circuit provides instantaneous fail-safe protection of the transmitter and load in the event of
even momentary interruption of the cooling water supply. This protection is necessary because dissipation of the
heat generated by the RF power absorption is critically dependent upon maintaining the required minimum water
flow rate regardless of inlet water temperature.
The water flow switch, attached to the water inlet of the load, is factory calibrated to open the electrical contacts
whenever the water flow drops below nine gallons per minute and close when the water flow exceeds this value.
When the water flow switch contacts open, the time delay relay switch is deactivated, which in turn opens the
interlock switch causing immediate shutdown of the transmitter or other signal source. The time delay relay also
keeps the interlock switch “open” for a 12 ±2 seconds interval after the minimum flow of nine gallons per minute
has been reestablished. This safeguarding feature assures proper operation of the cooling system before RF power
can be applied to the load, preventing damage or burnout of the resistive element.
The control assembly also includes a large light on top of the box. The red light should be freely visible from nearly
all front angles in the operating vicinity of the load unit/control assembly. After proper installation, as described in
, when the light is lit the RF load is ready to receive power, or when not lit indicates trouble
in the cooling supply (control).
