RLN42
Appendix: system overview of RN Series
Hauser
29
proof. A short-circuit and line break in the sensor line can be detected by the RLN42
evaluating unit. A NAMUR sensor does not need a separate power supply: its power is
supplied via the measuring circuit.
The operating voltage of the field loop in the "NAMUR measuring circuit" should be 8±1
Volt, and the load on short-circuit between 100 to 360 Ω.
NAMUR
sensors are operated with a transmitted current and have four states so that
sensor errors can also be detected by an analog evaluation unit. This is sometimes referred
to as the "closed circuit current principle".
NAMUR sensors can adopt four states at the output:
• Current of 0 mA: wire break; circuit open
• Current below 1.2 mA: sensor ready, undamped
• Current above 2.1 mA: sensor ready, damped
• Current of maximum value above 6 mA: short-circuit, maximum current
A common application of NAMUR sensors is limit value monitoring in process automation.
For this, analog signals are often only evaluated in a binary manner for a controller, e.g. if
the application involves monitoring the level in a tank or monitoring a temperature,
whereby a counteraction should be triggered if a limit value is exceeded. Here, the
temperature currently measured can only be used to determine whether the temperature
is above or below the limit value, for example.
The following are examples of typical applications of the RLN42 NAMUR isolating
amplifier. Each application is explained briefly and described in a schematic diagram.
Digital isolating amplification of NAMUR sensor signals from a hazardous area
• The passive Liquiphant FTL41 sensor with the FEL48 evaluation unit supplies a NAMUR
signal value 1.2 mA or 2.1 mA to the active input of the isolating amplifier
• The RLN42 NAMUR sensor active barrier isolating amplifier supplies a binary output
signal (relay contact), which depends on the input signal, to a digital input of the
controller
• Line breaks or short-circuits of the 2-wire sensor line are indicated by LEDs on the
RLN42
NAMUR
FEL 48
DI
Liquiphant
FTL41
PLC
NAMUR
Input
(1.2 or 2.1 mA)
Output
(binary)
24 - 230 V AC/DC
RLN42
Power supply
EX
EX
A0045919
12
NAMUR limit detection, Liquiphant FTL41 with FEL48 NAMUR evaluation in the hazardous area
Signal isolation of sensors with mechanical contacts from a hazardous area
• The FTE20 rotary paddle switch reports the state via a mechanical switching contact
• The sensor and the connecting cables are monitored for line breaks and short-circuiting
via the resistive coupling element, which is available as an accessory for the RLN42
• The RLN42 NAMUR isolating amplifier supplies a binary output signal, which depends
on the input signal, to a digital input of the controller
• Line breaks or short-circuits of the 2-wire sensor line are indicated by LEDs on the
RLN42