Regarding Namur signals and dry contact signals

The Namur signal operates on the principle of low-current detection (the specific current value can be found by searching on Baidu); it is one of the few intrinsically safe digital signals. A standard switch gate can accept both Namur signals and dry contact signals, with the wiring method remaining the same.

I checked – the Namur signal is powered by 8V from the safety barrier. So, when connecting a dry contact signal, what voltage does the safety barrier output?

A safety barrier can be understood as a fuse in electrical systems. It only serves a safety function in the instrument circuit. When a dry contact signal is received, the output is naturally a dry contact signal as well, with a voltage of 0.

NAMUR uses the magnitude of the current to indicate the position of the target (whether it is approaching or moving away), so there is no need to pay special attention to the value of the output voltage. The NAMUR probe itself contains an LC oscillation circuit, so it can generate a stable current once the valve is in position. The standard for NAMUR is IEC 60947-5-6; it was formerly known as DIN 19234. It specifies the signal interaction between the probe and the amplifier (referring to the safety barrier). For NAMUR used in intrinsically safe circuits, it is referred to as 8V/8mA NAMUR, indicating the open-circuit voltage and short-circuit current. The voltage level in the circuit is determined by the safety gate, while current limiting is achieved through the resistance of the safety gate, which is usually 1 kiloohm; therefore, connecting a passive switch will not cause a short circuit. IEC 60947-5-6 specifies the allowable ranges for these parameters. There are also a few 12V NAMUR devices available on the market, such as Emerson’s hybrid system DI, but they cannot accept 8V/8mA NAMUR sensors, like those from P+F.

Hello, Master. After doing some research, I found that for NAMUR signals powered by 8V, different current signals are generated depending on the distance of a metal object from the sensor: a current range of 2.1 mA to 6 mA corresponds to state 1 or ON, while a current range of 0.35 mA to 1.2 mA corresponds to state 0 or OFF. A circuit open fault is considered when the current is less than 0.28 mA, while a short-circuit fault is considered when it is greater than 6.5 mA. So, for DI dry contact signals, can I understand that when the dry contact is closed, an 8mA short-circuit current is supplied to the DI processing card, while when the dry contact is open, an open-circuit current of less than 0.28mA is supplied to the DI processing card? Then does the DI card process these two signals and send them to the controller for processing?

This post was last edited by HEJIYUER on 2020-1-31 02:32, version 1. The distance of a metal object from the sensor generates current signals of varying amplitudes; a current within the range of 2.1 mA to 6 mA corresponds to state 1 or ON, while a current within the range of 0.35 mA to 1.2 mA corresponds to state 0 or OFF. A circuit open fault is considered when the current is less than 0.28 mA, while a short-circuit fault is considered when it is greater than 6.5 mA. Answer: In NAMUR proximity switches (taking inductive sensors as an example), thanks to the built-in steady-state circuit, their output current (or rather, the current that forms a circuit with the associated safety barrier) is divided into four ranges. This allows distinguishing between an \"open circuit\" and a \"short circuit\" in the wiring. This is specified in the EN standards. The figure below shows a table linking the output voltage, current, and current-limiting resistor of the safety barrier, with the colored areas indicating the operating range. 2. So, for DI dry contact signals, can I understand that when the dry contact is closed, an 8mA short-circuit current is supplied to the DI processing card, while when the dry contact is open, an open-circuit current of less than 0.28mA is supplied to the DI processing card? Then does the DI card process these two signals and send them to the controller for processing? Answer: It can be considered that way, but the open-circuit current should be 0. The intrinsically safe 8V/8mA NAMUR safety barriers available on the market are typically designed with parameters of 8V/1 KΩ, and their short-circuit current is 8mA, as indicated by the red line below. 3. You can think of a NAMUR sensor as a switch plus series/parallel resistors: when the switch is closed, the impedance is low at 1K ohms, and when it is open, the impedance is high at 11K ohms. Therefore, a combination of a passive switch and a detection resistor can also generate current in the four areas, and it can be used in the trigger circuit of fire alarms (since fire alarm buttons are normally open, it is necessary to detect short circuits in order to avoid false alarms). 4. If no detection resistor is provided for the switch, then the \"open/short circuit detection function\" in the safety gate dialing/NAMUR IO configuration must be disabled; otherwise, alarms will continue to be generated. 5. The open-circuit voltage is 8V. Once a load is connected, the port voltage will drop; it’s around 5V in the case of a short circuit. However, you don’t need to worry about how the voltage changes – you just need to pay attention to the current. NAMUR is a two-wire circuit; the safety barrier must always have a voltage output, as the sensor contains electronic components that require a supply voltage in order to function. (Just like a 4-20 transmitter: as long as there is a working voltage, it’s fine; you don’t need to focus on exactly how much the voltage changes.) 6. The attachment is the schematic diagram of Texas Instruments’ NAMUR DI IO, which explains things quite clearly. You should be able to figure it out. . . . .

Thank you to the expert for sharing; thanks for the learning