Statistics on DCS points

Let that professional guy come and help answer it

LZ, your question is rather naive; if you’re not from the instrumentation field, this topic could indeed be discussed for an entire lesson. If you are in the instrumentation field, this question is not difficult at all. Let me explain in detail: 1. How to determine the number of points in instrument installation – the volume of work is not determined by the number of points! 2. The pressure gauge is a field-mounted device; procurement is related to the instrument itself, while installation is related to piping work! 3. Control valves with interlocks: Control valves cannot be used as interlock actuators! The composition of the 4 instrument circuits is not one-to-one; sometimes one input point can correspond to multiple circuits, enabling it to perform its function in those multiple circuits! 5. On-site instrument testing is carried out by the instruments themselves; installation, however, remains the responsibility of the piping team! 6. Local valves are what we call process valves, while the valves used in instruments are collectively referred to as control valves, including control valves and on-off valves! 7. How can a safety valve be confused with a safety barrier! Does LZ mean DCS terminal? Then that’s correct.

The DCS points refer to the total number of outputs and inputs in DCS.

I would also like to ask: the control valve is equipped with a pneumatic or electric actuator, and it should be interlocked with signals such as flow rate and liquid level via a DCS – this is a requirement in terms of process design Also, the statistics on points or circuits are important indicators used during circuit testing and debugging after the installation of the instruments, right?

The points of instruments are divided into input points and output points, including DI, DO, AI, and AO, which can be counted according to the inputs and outputs of the DCS.

I really don’t understand the poster’s reasoning; when it comes to tracking points in DCS, you need to know where the signals entering and leaving DCS come from, and what type of signals they are. You know that valves are subject to things like flow control and even interlock switches; you should be able to determine on your own the number and type of signals that need to be sent to or from the DCS.

There’s really no other way; count the pairs of wires entering and leaving the DcS card modules – whether they are entering or leaving, one pair counts as one.

Does the poster think that all valves equipped with an actuator are control valves? In fact, those on-off valves also fall within the operating range of instruments; such valves serve as actuators in interlock logic.

I’ve learned it; thanks to everyone up above for their help. :victory:

I think for this issue, it’s sufficient to understand the classification of instrument points; there’s no need to worry about whether there is a linkage or not. Just figure out the types of instrument signals that go in and out of the DCS cards, regardless of what kind of instruments are used on site.

The DCS point count is determined based on the \"process flow diagram with control points\" or the actual number of input/output points. During the preliminary design phase, the former is used as a basis, to which a redundancy factor of around 10%~15% is added.

As I understand it, you want to know how the number of control points in DCS is calculated. For detection signals such as temperature, pressure, liquid level, flow rate, etc., as long as there is a value for such a signal in the DCS, it is counted as one point (regardless of whether that signal is used for display, control, or other purposes in the computer). The same applies to the outputs of the DCS – each value is counted as one point. The calculation of these points is generally related to the purchase of cards used in the DCS, and it is different from the number of control loops. Regarding what LZ said, “Could it be similar in terms of the number of terminals on the safety valve’s safety barrier?” ”Can’t understand.

Interlocking is also achieved through control valves. An electromagnetic valve is installed in the air circuit of the control valve; a signal is sent to the relay via the output of the interlock circuit, and by turning the electromagnetic valve on or off, the air supply to the control valve is cut off, thereby putting the control valve in either an open or closed state and ensuring that the process and equipment remain in a safe condition.

The points of DCS are divided into: DI for digital input, DO for digital output, AI for analog input, and AO for analog output. Signals from pressure instruments and similar devices are generally in the range of 4–20 mA, and they belong to AI signals ； The points for opening and closing the valve should be represented by DO signals; depending on the electrical design, the opening signal can be one point or two points. The feedback of digital signals such as contactors and limit switches belongs to DI signals. Typically, control actuators use 4–20mA signals, which are sent out by DCS cards; such signals belong to the AO category. I wonder if you can understand it if I put it this way?

I’ve learned it; once again, thank you. :)

Whether it’s a signal entering the DCS or leaving it, any signal counts as a point; if you’re not sure, just count the cables – one pair of signal wires constitutes one point.