SERIES 80 CONTROL CIRCUITS
APPLICATION
Series 80 is the low-voltage equivalent of Series 40. It is suited for applications requiring low-voltage, two-position control of two-wire circuits by single-pole, single-throw controllers.
Series 80 has two advantages over Series 40:
1. Since contacts of Series 80 controllers are required to carry less current, the controller mechanism can be physically smaller than a Series 40. The controller there- fore has less lag and the capability to have a narrower differential.
2. Low-voltage wiring (when not in conduit or armor) costs less than line-voltage wiring.
EQUIPMENT
CONTROLLERS
1. Temperature controllers.
2. Humidity controllers.
3. Any low-voltage device with a minimum of one normally-open contact such as a low-voltage relay.
A Series 80 controller cannot switch line voltage directly. A relay must be used between the controller and a line-voltage load. However, Series 40 or Series 80 controllers can be used with Series 80 actuators.
A Series 80 controller has snap-acting contacts or a mercury switch. Some Series 80 controllers are three-wire, double-throw devices as in heating-cooling thermostats.
Many Series 80 heating thermostats have internal adjustable heaters in series with the load. This provides enough artificial heat during the on cycle to cause the sensing element to open the switch on a smaller rise in space temperature. Some Series 80 cooling thermostats have a fixed heater which energizes when the cooling circuit is deenergized. This provides artificial heat to the sensing element to close the switch on a small rise in space temperature. This cooling and heating anticipation (also called time proportioning) provides close space-temperature control. See the Control Fundamentals section.
RELAYS AND ACTUATORS
Relays and actuators are similar to those of Series 40 except that they operate on low voltage.
OPERATION
Figure 10 illustrates a simple Series 80 circuit. This is the same as a Series 40 circuit with the added transformer.
CONTROL COMBINATIONS
Series 80 control combinations are similar to those of Series 40. The following applies:
1. Series 80 circuits require an external, low-voltage
2. Series 80 equipment can be controlled by Series 40 or 80 controllers.
3. Series 80 controllers can control line-voltage actuators or other line-voltage devices by using a Series 80 relay with line-voltage contacts.
HIGH-LIMIT CONTROL
A Series 80 valve with high-limit controller is shown in Figure 11. The transformer supplies 24V ac to the circuit. The thermostat controls the heating valve actuator. The high-limit controller opens the circuit on a temperature rise to the high- limit setting. Contacts on both controllers must be closed to open the valve.
LOW-LIMIT CONTROL
Same as for Series 40 except that a transformer and a Series 80 actuator are used. See Figure 9.