Safety barrier selection
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Safety barrier requirements: For input parameters – Input current: range of 4~20mA; supply voltage: none. For output current: range of 4~20mA; supply voltage: none. Allowed load: ≤500Ω. Is there such a safety barrier? In simpler terms, it should have input and output signals of 4-20MA, with no need for 24V supply on either side. The operating voltage of the safety barrier doesn’t matter. Currently, my instrument outputs 4-20MA signals and is powered by 24V; my DCS card is also powered by 24V. Can I use the safety barrier mentioned above without making any changes to the hardware?
LB930 Longfei. . . . . . . . . . .
Every company has such products! For example, Zener type
Reply to 1# sumingdefeng: I have safety barriers from Knick in Germany; they don’t require a separate power supply circuit, as they are powered directly by the output signal circuit.
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We use P+F and MTL here, and the performance is quite good!
Zhejiang University Zhongkong SB3045-Ex series isolated safety barriers, signal transmission: 4-20mA, operating voltage: DC24V
With P+F safety barriers, the wiring terminals for 4–20mA input vary depending on whether power supply is provided or not; the output options include 4–20mA and 1–5V. I haven’t heard of any concept related to power distribution – to whom is the power supplied, to secondary instruments or to DCS input modules? Secondary instruments and DCS input modules generally also have two connection methods: with power supply and without power supply; once a safety barrier is used, power supply is not provided.
The safety barrier itself requires electricity to function; it takes in a signal of 4–20mA and outputs a signal of 4–20mA as well. As for whether the output should be powered or not, different connection methods can be chosen. In short, the safety barrier itself uses two wires for operation: two signal wires are connected to the input side of the safety barrier, and another two signal wires are connected to its output side. It’s just six wires.
What was said upstairs is correct – safety barriers need power to function. There are various ways to provide this power; some safety barriers can be powered through the output signal circuit, without the need for a separate power supply. The wiring method is as follows:
This is a safety barrier based on traditional standards. It was only later that safety barriers with power distribution functions and opto-isolated versions were developed.