Namur principle

We would like to tell you a bit about the principle of NAMUR sensors.

NAMUR sensors are normally used in explosive areas (only with a NAMUR switching amplifier). They are always 2 wire sensors.
They do not have a switching output like “normal” sensors.
NAMUR sensors are operated with an impressed current and have four states, so that the error cases of the sensors can also be detected by an analog evaluation unit.

This is also referred to as the quiescent current principle.
 

                                                                  With normally open contact (NO)               With normally closed contact (NC)

1. current of 0 mA                              ⇒ wire break, circuit open                            ⇒ wire break, circuit open
2. current of less than 1.2 mA            ⇒ sensor ready, undamped                          ⇒ sensor ready, damped
3. current above 2,1 mA                     ⇒ sensor ready, damped                              ⇒ sensor ready, undamped
4. current of maximum value             ⇒ short circuit, maximum current                ⇒ short circuit, maximum current.

The operating voltage of the field loop should be ~ 8.2 VDC

The following equivalent circuit can help.

Namur sensors are special 2-wire sensors without an output stage. These are usually evaluated by external switching amplifiers and are classified in this combination by their ignition protection type as "intrinsically safe Ia". The switching amplifier transforms current changes into a binary output signal.
Our amplifiers are these:
EN2-2EX1 # 6041096
EN2-2EX3 # 6041095

The amplifiers have to be installed outside the explosive area.