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Requirements for Instrument Installation and Use in DCS System

In order to ensure the operation quality of DCS system, the instrument signal input to the system must be accurate. Therefore, it must be installed correctly in strict accordance with gbj93-96 "automatic control installation atlas" and instrument operation manual. The requirements for the installation and use of instruments are as follows.

Pressure transmitter

1. Since the pressure tapping device for pressure and negative pressure is installed on the pipeline in the straight direction of the flow beam, it shall not be installed in the bending, corner, dead angle and vortex of the beam, which are enough to distort the static head.

2. When installing the pressure tapping device for pressure or negative pressure, because it is perpendicular to the flow beam, the pressure tapping pipe shall not extend into the interior of the fluid pipeline or equipment. The pressure tapping port shall have a smooth outer edge without sharp edges. The continuously used conduit and accessories shall be neatly cut and deburred.

3. The installation position of pressure tap on horizontal and inclined pipelines shall be at the upper part of the pipeline when the fluid is gas.

When the fluid is liquid, the lower half of the pipeline is within the included angle range of 0-450 from the horizontal centerline or on the centerline of the pipeline. When the fluid is steam, the upper half of the pipeline is within the included angle range of 0-450 from the horizontal centerline or on the centerline of the pipeline.

4. All pressure tapping devices must be equipped with primary doors, which shall be close to the pressure tapping device.

5. The horizontal section connecting the impulse pipeline shall maintain a certain slope, and the inclined direction shall ensure the discharge of air or condensate. The gradient of the pipeline is required, and the pressure pulse pipeline is not less than 1:100. A blow down valve shall be installed at the pressure gauge of the pressure pulse pipeline to flush the pipeline and exhaust air.

6. The impulse pipeline shall be purged before installation to ensure that the pipeline is clean and unblocked. The valves on the pipeline shall be subject to tightness test before installation. After the pipeline is laid, the tightness test shall be conducted again. Before start-up, fill the impulse pipeline with water (note that bubbles are not allowed to pour in during water filling to affect the measurement).

7. For the placement of smart transmitter, please refer to the attached transmitter placement and operation manual.

Temperature transmitter

1. The temperature sensing element shall be placed at a place that can represent the temperature of the measured medium, and the temperature sensing element shall not be placed near the valve, elbow and dead corner of the equipment. The temperature sensing element should be placed obliquely, and its inclined direction should make the temperature sensing end face the fluid.

2. When installing heat sensing elements on pipes with diameter less than 76mm, the method of expanding the pipe shall be adopted.

3. In order to facilitate disassembly and prevent dirt from falling into the thermometer, platinum resistance thermometer is installed on the horizontal pipe, which is generally installed horizontally or slightly downward.

4. The temperature sensing part of platinum resistance thermometer shall be installed at the center of the pipe, and the distance between the temperature end and the pipe center shall be 50-70mm.

electromagnetic flowmeter

1. The environmental conditions (temperature, humidity, electromagnetic field, etc.) of the installation location must meet the requirements of the manual.

2. Length of straight pipe section. According to the situation of the pipeline where the flowmeter is located, the necessary straight pipe length must be ensured. Generally, the upstream pipeline maintains a straight pipe section of more than 10d and the downstream pipeline maintains 3D-4D. D is the pipe diameter.

3. The addition of chemical additives will affect the liquid conductivity and should not be injected upstream of the instrument. If it must be injected upstream, the reactor or straight pipe section with sufficient volume must be maintained to make the liquid conductivity flowing through the flowmeter stable.

4. Installation method: regardless of horizontal, vertical and inclined installation, it must ensure that the measuring pipe of the instrument is always filled with liquid and there is no bubble (see the instrument manual). For solid particles or slurry, it is recommended to install vertically, with the flow direction from bottom to top. The plane of the electrode must be parallel to the ground.

5. Grounding a. the working grounding of the flow sensor is to ensure that the reference potential is the same as the measured body, and the liquid level potential should be the same as the ground potential. The electromagnetic flowmeter is equipped with a grounding ring, which is used to establish liquid grounding through contact with liquid. According to the different pipeline materials where the flowmeter is located, the grounding connection mode shall be correctly adopted. The working grounding shall adhere to the principle of "single point grounding". (refer to the article "grounding measures for electromagnetic flowmeter" on page 48-49 of the fourth issue of "chemical automation and instrumentation" in 1998) the grounding resistance shall be ≤ 100 ohms. B. Shield grounding. The shielding layer of the signal cable output from the flow converter to the secondary instrument DCS system is grounded at one side of the control room and through the grounding busbar.

6. Reasonable process procedures and correct operation. Prevent bubbles generated in the production process from flowing through the electromagnetic flowmeter.

Vortex Flowmeter

1. Pipe support: if there is vibration in the pipeline, it shall be supported.

2. Installation: if the pipeline is filled with liquid, the Reynolds number is greater than 2 × 104, the pipeline can be installed vertically or at an inclined angle.

3. Valve position and straight pipe length A. generally, install the flowmeter upstream of the valve. The length of straight pipe before and after flow is > 20d and > 5D respectively. B. Install the valve upstream of the flowmeter: for the air pipeline using piston or roots blower and compressor or the high-pressure liquid pipe (about more than 1MPa) using piston or plunger pump, liquid vibration may occur. In these cases, the valve can be installed upstream of the flowmeter. At this time, the length of the straight pipe between the flowmeter and the valve shall be greater than 20d, and the length of the straight pipe downstream of the flowmeter shall be greater than 5D.

4. Length of elbow and straight pipe section: the straight pipe section length of 20d shall be ensured upstream of the flow. If a gate valve is installed upstream of the flowmeter, a straight pipe length of at least 20-40d shall be guaranteed upstream.

5. Length of reducing, expanding and straight pipes: the upstream of the flowmeter shall ensure the straight pipe length of 10d, and the downstream shall ensure the straight pipe length of 5D.

6. Pressure measuring point: take the pressure measuring point between 2-7d at the downstream side of the flowmeter.

7. Temperature measuring point: take the temperature measuring point between 1-2D distance at the downstream side of the temperature measuring point.

Dynamic concentration transmitter

(1) Installation of transmitter

1. Position a. the installation position of the transmitter shall avoid mechanical damage and vibration. The electronic unit shall be installed in a cool and ventilated place to prevent slurry. It is recommended to install a waterproof baffle on it. B. The transmitter shall be installed as close as possible to the measuring point at the dilution water connection to ensure the shortest time lag. C. The transmitter can be installed on vertical and horizontal slurry pipes. The vertical position transmitter shall be perpendicular to the axis of the pump, and the horizontal position shall be installed on the side of the slurry pipe. It is recommended to install in a vertical position as far as possible.

2. Distance a. the installation position of the transmitter shall consider the minimum stable distances L1 and L2 of the front and rear slurry pipes. Generally, L1 = 10d, L2 = 5D, D - pipe diameter. According to the actual flow and concentration, the length of L1 can also be estimated by using the attached drawings of the instrument operation manual, L2 = L1 × 0.30.3。 B. The estimation method is suitable for chemical pulp and long fiber pulp. If it is waste pulp, ground wood pulp and staple fiber pulp. The result of the above estimate is multiplied by 1.25.

3. Connect the short pipe. When installing the transmitter to connect the short pipe, pay special attention to the distance h = 20-22mm from the blue mouth of the short pipe method to the inner wall of the slurry pipe. If the short pipe is processed and connected according to the adhesive paper provided with the equipment, the short pipe shall be added to the slurry pipe, but ensure that the inner wall of the slurry pipe is flush and welded without bulge.

4. Slurry pipe: if the slurry pipe is made of carbon steel and other materials, it is difficult to weld. It is recommended to select a 1m long stainless steel pipe to install the transmitter, and the connecting short pipe is welded at the center.

5. Transmitter sensing element A. do not mechanically collide with the blade, and do not lift the transmitter with manual blade or force. B. The blade shall be installed parallel to the slurry pipe and consistent with the slurry flow direction.

6. Transmitter wiring A. all signal cables connected to the junction box must be 1.3-1.5mm2 multi-core shielded cable. B. All cables shall be protected by galvanized steel pipes or cable sleeves, and power and signal cables must be protected by pipes respectively.

(2) Installation of, sampling valve and dilution water valve

1. Sampling valve: the installation position can be selected below the transmitter for convenient operation.

2. Dilution water pipe a. the installation position of dilution water valve shall be as close to the dilution point as possible. B. The dilution water pipe shall be vertically inserted into the suction side of the slurry pump for 15-50mm, and the water pipe is located between the slurry tank and the slurry pump, 1 / 3 away from the slurry pump. C. The dilution water pipe shall be capable of producing a flow rate of about 5m / s at the connection. D. The dilution water pressure shall be stable. It is recommended to install a pressure gauge on the water pipe.

Flange type liquid level transmitter

1. The transmitter shall be installed at another position at the bottom of the tank where the liquid level needs to be measured (it shall not be connected to the method port).

2. The transmitter shall be installed at the place where the liquid is relatively stable, avoiding and far away from the turbulence equipment (such as agitator, slurry pump, etc.).

Suggestions on prevention and control of electromechanical interference

1. Power wires and measuring wires shall be installed in completely separate metal wire bridges, which shall be connected together and grounded every 100m. At least 2m distance shall be ensured between two wire bridges of different properties.

2. The force switchgear shall be as far away from the instrument system as possible, and at least use a separate support.

3. For the electrical shielding of instruments, the principle of "Faraday closing" shall be applied: there shall be complete and connected shielding around the conductor. The electrical shield shall be heavy woven (covering 80%), and the electrical shell or shielding layer can only be grounded at one end (generally connected to the power supply end) and continuously connected through the grounding box or cabinet.

Quantitative valve

a) The quantitative valve with a diameter of 50-250mm can be installed on vertical, horizontal and inclined pipes. 300mm-350mm shall be installed on the horizontal slurry pipe, and the adjustment machinery shall be upward.

b) Clean the slurry pipe before installing the valve to ensure that there are no sundries on the slurry line and prevent mechanical damage to the quantitative cutting and sealing ring. The arrow direction of the cutting body is consistent with the slurry flow direction. The electronic unit can be installed near the metering station or in the control room. It shall avoid mechanical damage and vibration, be waterproof and slurry proof, and the ambient temperature shall not exceed 40 ℃

Input type liquid level transmitter

1. When installing in still water, such as deep well and pool, the method of inserting steel pipe is generally used. The inner diameter of steel pipe is Ñ„ About 45 mm, the steel pipe shall be drilled with several small holes at different heights to facilitate the smooth entry of water into the pipe.

2. When installing in flowing water, such as water channel and non-stop mixing water, insert the inner diameter in Ñ„ For the steel pipe of about 45mm, several small holes shall be drilled at different heights on the opposite side of the water flow direction to make the water enter the pipe.

3. The transmitter shall be installed vertically downward, and the transmitter shall be placed away from the liquid inlet and outlet and the mixer.

4. If necessary, the steel wire can be wound around the transmitter and vibrated up and down with the steel wire to avoid breaking the cable.

L-type three-way valve

Before installation, carefully confirm the valve model, specification and flow path switching, and install the valve in strict accordance with the valve instructions. Prevent the continuous phenomenon of connection and disconnection after taking over.

Requirements for Instrument Installation and Use in DCS System 1

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