Page 124 - Sensors and Control Systems in Manufacturing

Classification and Types of Sensors
(+) (–) 85
Load Load

Load

FIGURE 2.73 Transistor switch. FIGURE 2.74 Voltage clamp.

the transistor. Peak voltage clamps such as zener diodes or transorbs
are utilized to protect the output device. Transistor outputs are
typically rated to switch loads of 250 mA at 30 V DC maximum
(Fig. 2.74).
The following outlines the advantages and disadvantages of
transistors.

Transistor Advantages Transistor Disadvantages
Virtually instantaneous response Low current handling capacity
Low OFF state leakage and Cannot handle inrush current
voltage drop unless clamped
Infinite life when operated within Can be destroyed by short circuit
rated current/voltage unless protected
Not affected by shock and
vibration

2.9.3.1 Output Configuration
Output configurations are categorized as follows:

• Single output—normally open (NO)
• Single output—normally closed (NC)
• Programmable output—NO or NC
• Complementary output—NO and NC

The functions of normally open and normally closed output types
are defined in Table 1.8.

2.9.4 Inductive and Capacitive Control/Output Circuits
A single output sensor has either an NO or an NC configuration and
cannot be changed to the other configuration (Fig. 2.75).
A programmable output sensor has one output, NO or NC,
depending on how the output is wired when installed. These sensors
are exclusively two-wire AC or DC (Fig. 2.76).