EFST-6 is an alarm thermostat for use as electronic frost protection of water-based heating and ventilating systems. The thermostat is able to open a valve via a DC regulating signal before a frost alarm condition is reached.

Electronic monitoring of heating surface in heating and ventilating systems
Adjustable alarm temperature
Two relay outputs, 1 change-over contact, 1 switch on contact
Temperature sensor independent of location of thermostat
Relay output will be cut out if the sensor is short-circuited/disconnected
DC output for read-out of sensor temperature
Fixed T (4°C) or variable T (5-40°C) setpoint
To be connected to the system temperature regulator (0-10V DC)

Product Range

	Product	EAN-Nr
EFST-6-1221	Frost thermostat, 230V, scale 0-20°C	5703502510170
EFST-6-3221	Frost thermostat, 24V, scale 0-20°C	5703502510187
Accessories
ETF-.22	Temperature sensor, various types

Function
During normal operation the two output relays of the frost thermostat are normally activated. If the sensor temperature drops below the preset alarm temperature (TA), the relays cut out. This activates the alarm, and the red LED lights. At the same time a relay, via the main control system, cuts out the fan and closes the damper.

The alarm can be manually reset by activating the reset button or by breaking the power supply. The DC-regulated output from EFST-6 can be used to take over the control of the valve if the temperature drops below the preset alarm temperature (TA) plus an adjustable differential (T). Thus it is possible to prevent the temperature dropping below the alarm setpoint, which, in turn, results in the system being shut down.

By setting T (see example) and removing the link between terminals 11 and 14, EFST-6 may be used as a night setback thermostat and will maintain the temperature at above the frost condition level. This also ensures that the temperature of the return water from the heater battery is at a certain level when the system is started in the morning.

Example: With a control regulator connected across terminals 13 and 14, and if the alarm temperature (TA) is set to 8°C and the valve is to be activated once the temperature has fallen below 25°C, T must be set to 17°C. The valve will then modulate between 25°C (closed) and 8°C (open). With terminals 11 and 14 linked, T will be fixed at 4°C. Once the temperature in the system has risen above TA + T, the regulator of the system will take over control. A choice of four control signals used by the regulator of the system can be selected by DIP switches on EFST-6.

Safety function
An alarm is given if the sensor cable is disconnected or short-circuited. Monitoring function EFST-6 has a 0-10V output signal for external read-out of sensor temperature (0-40°C)

Technical data

Supply voltage	24V AC, 230V AC ±10%, 50-60 Hz
Power consumption	3 VA
Ambient temperature	-10/+50°C
Alarm temperature	TA setting 0-20°C
Delta T setting	4°C fixed (terminal 11 and 14 linked)
Delta T setting	5-40°C
Accuracy	±5% for the scale range
Output signal to valve	Output signal to valve
Instrument output	0-10V DC, max. 10 mA
Relay outputs	1 S.P.S.T. & 1 S.P.C.O. 250V / 6A resistive load
Weight	180 g
Dimensions L x W x D	86 x 52.5 x 58 mm
Housing	IP 20