How to calculate DCS system points

October 08,2024

How to calculate DCS system points

DCS control system points is a lot of self-control system and the use of self-control system manufacturers need to consider the issue of DCS system points is the number of input points, the number of output points and system points and the total number of communication points.

DCS system points from the analogue input points, analogue output points, digital input points, digital output points and DCS and other system communication points from five statistical aspects.

1, how to calculate the analogue input points

Analogue input refers to the analogue input signal into the DCS system or PLC system. Can be divided into the following cases:

--Thermocouple input point statistics

Single mounted thermocouple or single armoured thermocouple is counted as 1 point;

Double assembled thermocouple or double armoured thermocouple need to display two sensor temperatures of the same measurement point in the DCS system is counted as 2 points, and only one temperature of that measurement point is counted as 1 point;

Single multi-point thermocouple or multi-point thermocouple is often used to monitor the same measurement point of different parts of the temperature, thermocouple has a few measurement points will be calculated for several points of thermocouple input.

-- RTD input point count with thermocouple

--Standard current 4 ~ 20mA, voltage input and other analogue input signals, a detection instrument to send in the information, point statistics calculated according to 1 point

2、How to calculate the number of analogue output points

Analogue output is the analogue signal sent to the site by the control system. Generally 4-20mA, 0-20mA, 0-5V, 1-5V and 0-10V five types, regardless of which case, the analogue output of a signal output is calculated as 1 point.

3、How to calculate the number of digital input points

Digital input signal, whether dry contact or wet contact (passive or active) for the system is a digital input counted as 1 point

4, how to calculate the number of digital output points

Digital output signals, is the control system to send digital signals to the scene, DCS system control of different devices which require different DO output points

--Pump control, such as general signals to be sent to the electrical, electrical will generally want two signals a turn, a stop then need 2 digital output points.

--Solenoid valve control, power on (off), power off (on) 1 digital output can be.

5. How to calculate the number of communication points?

Communication point is a control system and other control systems or equipment through the communication technology (such as MODBUS, OPC, etc.) contact point, we are accustomed to call the soft point. The calculation method of communication point is very simple, regardless of AI, AO, DI, DO and various devices, a contact is counted as a point. For example, other systems have 10 digital points of communication to the system, then count 10 points.

Here are two commonly used devices point counting for your reference:

Switching electric actuator.

--Each actuator valve position feedback 4-20mA counting AI input 1 point;

--Valve forward/reverse control calculation of digital output 2 points;

--Valve open in place/valve close in place signal calculation digital input 2 points;

--Valve open over-torque/close over-torque fault signal calculation digital quantity input 2 points.

Frequency converter:

--Frequency feedback calculation AI input points 1 point for each inverter;

--Frequency given signal calculation AO output 1 point;

--Run/stop given command calculation DO output 1 point;

--Inverter fault alarm calculation DI input 1 point;

--Fault reset calculation 1 DO output 1 point;

-- Inverter running status calculates 1 point of DI input.

--If the frequency converter is connected to DCS system with communication mode, only 1 communication point needs to be calculated, no other points need to be calculated.

--If DCS system is connected with external solenoid valve, indicator, contactor and other devices, calculate 1 point of DO output for each device.

Translated with DeepL.com (free version)

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