How Electric Control Circuits Are Classified - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

Damper: A device used to control the flow of air in a duct or
through a wall louver.
Line voltage: A term which refers to the normal electric supply
voltage. Line voltage can be used directly in some
control circuits or can be connected to the primary
side of a step down transformer to provide power for
a low-voltage control circuit. Most line-voltage
devices function at their rated voltage +10%/–15%.
Line-voltage devices should be tested and listed by
an appropriate approval agency.
Linkage: A device which connects an actuator to a damper or
control valve. To open and close a damper, the typical
linkage consists of an actuator crankarm, balljoints,
pushrod, and damper crank arm. In a valve application,

HOW ELECTRIC CONTROL CIRCUITS ARE CLASSIFIED

There are seven basic electric control circuits, each of
which has unique characteristics. These control circuits are
identified by Series Numbers 10, 20, 40, 60, 70, 80, and 90
(Table 1). Series 10 and 20 are no longer used. Series 70 is
electronic control and is covered in the Electronic Control
Fundamentals section.
Series Controller
40 Line voltage, spst. Makes circuit
when switch is closed, breaks it
when switch is open.
60 Line voltage spdt equivalent of
Two position Series 40
60 Line voltage spdt with center
Floating neutral or dual Series 40
80 Low voltage, spst equivalent of
Series 40.
90 Low voltage. Proportional action
Table 1 lists and describes the basic control circuits. These
basic circuits are frequently expanded to provide additional
features such as:
1. High-limit override or control.
2. Low-limit override or control.
3. Minimum/maximum positioning of dampers and valves.
4. Manual reset.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
Low voltage: A term which applies to wiring or other electrical
Relay: A device consisting of a solenoid coil which operates
Transformer: A device used to change voltage from one level
the requirements for the basic series for which it is intended.
However, there are many applications which incorporate
controls of different series in the same control circuit.
Table 1. Honeywell Electric Control Circuits.
Signal Circuit
Two-wire, line voltage
Three-wire, line voltage Any Series 60 actuator
Three-wire, low voltage
Two-wire, low voltage
Three-wire, low voltage
more common applications. To make it easier to understand
the control circuits, the simplest circuits (i.e., Series 40) are
presented first.
99
ELECTRIC CONTROL FUNDAMENTALS
the linkage connects the actuator to the valve and
translates the rotary output of the actuator to the linear
action of the valve stem.
devices using 30 volts or less. Low-voltage control
devices usually function on 24V ac +10%/–15%.
load-carrying switching contacts when the coil is
energized. Relays can have single or multiple contacts.
to another. For control circuits this is usually line
voltage to low voltage. Transformers can be used only
on ac power.
The construction of individual control devices conforms to
Actuator/Relay
Any Series 40 actuator
or load
or load
Any Series 60 actuator
Any Series 80 actuator
or load
Any Series 90 actuator
The following paragraphs illustrate and discuss some of the
Control Mode
Two-position
Two-position, reversible
Floating, reversible
Two-position
Proportional