Precautions for the Installation of Automatic Instruments in Refrigeration Devices (Part Two)

2025-05-06

I. Temperature Detection Instruments

The temperature measuring elements of contact-type temperature detection instruments such as thermometers, thermal resistors, and thermocouples should be installed at the position where the temperature of the measured object can be accurately reflected.
If the temperature measuring element is installed at a position vulnerable to the strong impact of the measured material, anti-bending measures should be taken as specified in the design documents.
The temperature sensing surface of the surface thermometer should be in close contact with the surface of the measured object and should be firmly fixed.
The temperature bulb of the pressure thermometer should be fully immersed in the measured object.
II. Pressure Detection Instruments
The pressure gauge installed on site should not be fixed on equipment or pipelines with strong vibration.
The installation height of the pressure gauge or transmitter for measuring low pressure should preferably be the same as the height of the pressure tapping point.
When the pressure gauge for measuring high pressure is installed near the operation post, it should preferably be more than 1.8 meters away from the operation surface, or a protective cover should be added in front of the instrument.
III. Flow Detection Instruments
The installation of the throttling element should meet the following requirements:

Appearance inspection should be carried out before installation. The inlet edge of the orifice plate and the outlet edge of the nozzle should have no burrs, rounded corners, and visible damage, and the manufacturing dimensions should be measured and verified according to the design data and manufacturing standards.
Cleaning should be carried out before installation, and the throttling element should not be damaged during cleaning.
The throttling element must be installed after the pipeline is purged.
The installation direction of the throttling element should make the fluid flow from the upstream end face of the throttling element to the downstream end face.
The sharp edge of the orifice plate or the curved surface side of the nozzle should face the flow direction of the measured fluid.
For the orifice plate or nozzle installed on a horizontal and inclined pipeline, when there is a drain hole and the fluid is liquid, the position of the drain hole should be at the top of the pipeline; when the fluid is gas or steam, the position of the drain hole should be at the bottom of the pipeline.
The side of the ring chamber with the “ ” mark should be on the upstream side of the flow direction of the measured fluid. When the flow direction is indicated by an arrow, the direction of the arrow should be consistent with the flow direction of the measured fluid.
The end face of the throttling element should be perpendicular to the pipeline axis, and the allowable deviation should be 10.
The inner diameter of the sealing gasket for installing the throttling element should not be smaller than the inner diameter of the pipeline, and it should not protrude into the inner wall of the pipeline after being clamped.
The throttling element should be coaxial with the pipeline or the clamping piece, and the misalignment error between its axis and the axes of the upstream and downstream pipelines should comply with the following formula:
Where: ex —— Axis error;
D —— Inner diameter of the pipeline;
β —— The ratio of the inner diameter of the throttling element to the inner diameter of the pipeline under working conditions.

The connection between the positive and negative pressure chambers of the differential pressure gauge or differential pressure transmitter and the measuring pipeline should be correct. The inclination direction and slope of the pressure guiding pipe, and the installation of the isolator, condenser, settler, and gas collector should all comply with the provisions of the design documents.
The rotameter should be installed on a pipeline without vibration.
The included angle between its center line and the plumb line should not exceed 2°. When installed vertically, the flow direction of the measured fluid should be from bottom to top, and the length of the upstream straight pipe section should not be less than twice the diameter of the pipe.
The center of the target of the target flowmeter should be concentric with the pipeline axis, the target surface should face the flow direction and be perpendicular to the pipeline axis, and the lengths of the upstream and downstream straight pipe sections should comply with the provisions of the design documents.
The signal line of the turbine flowmeter should use a shielded wire. The lengths of the upstream and downstream straight pipe sections should comply with the provisions of the design documents, and the distance between the preamplifier and the transmitter should not be greater than 3m.
The signal line of the vortex street flowmeter should use a shielded wire. The lengths of the upstream and downstream straight pipe sections should comply with the provisions of the design documents. When the amplifier is installed separately from the flowmeter, the distance between the amplifier and the flowmeter should not exceed 20m.
The installation of the electromagnetic flowmeter should comply with the following provisions:

The flowmeter housing, the measured fluid, and the pipeline connection flange should be connected as an equipotential and should be grounded.
When installed on a vertical pipeline, the flow direction of the measured fluid should be from bottom to top. When installed on a horizontal pipeline, the two measuring electrodes should not be at the top and bottom positions of the pipeline.
The length of the upstream straight pipe section of the flowmeter and the installation support method should comply with the provisions of the design documents.

The scale dial of the oval gear flowmeter should be in a vertical plane. When the oval gear flowmeter and the Roots flowmeter are installed on a vertical pipeline, the flow direction of the fluid in the pipeline should be from bottom to top.
The lengths of the upstream and downstream straight pipe sections of the ultrasonic flowmeter should comply with the provisions of the design documents. For a horizontal pipeline, the position of the transducer should be within the range of an included angle of 45° with the horizontal straight line. The inner wall of the measured pipeline should not have a scaling layer or coating that affects the measurement accuracy.
The installation of the averaging pitot tube flowmeter should comply with the following provisions:

The total pressure measuring hole should face the flow direction, and the angular deviation should not be greater than 3°.
The detection rod should pass through and be perpendicular to the pipeline center line, and the deviation from the center and the deviation from being perpendicular to the axis should not be greater than 3°.
The lengths of the upstream and downstream straight pipe sections of the flowmeter should comply with the provisions of the design documents.

The installation of the mass flowmeter should meet the following requirements:

It should be installed on a pipeline that is completely filled with the measured fluid.
It is preferably installed on a horizontal pipeline. When measuring gas, the box tube should be placed above the pipeline; when measuring liquid, the box tube should be placed below the pipeline.
When the measured fluid on the vertical pipeline is liquid, the flow direction of the fluid should be from bottom to top.
The support installation method should comply with the provisions of the design documents.
IV. Level Detection Instruments

The installation height of the buoyancy level gauge should comply with the provisions of the design documents.
The installation of the float level gauge should make the float in a vertical state, and the allowable deviation of verticality should be 2mm/m. The center of the float should be at the height of the normal operating liquid level or the boundary liquid level.
The guide tube of the steel tape level gauge should be installed vertically, and the steel tape should be at the center of the guide tube and slide freely.
When measuring the liquid level with a differential pressure gauge or differential pressure transmitter, the installation height of the instrument should not be higher than the lower pressure tapping port. When measuring the liquid level with a double-flange differential pressure transmitter, the air blowing method, and the method of using the vaporization of a low-boiling liquid to transmit pressure, this article is not applicable.
V. Control Instruments and Integrated Control Systems
During the unpacking and handling of various control, display, recording instruments, auxiliary units, and integrated control systems installed in the control room, there should be no severe vibration, and dust and moisture should not enter the equipment.
The following conditions should be met before the installation of the integrated control system equipment:

The foundation base should be installed.
The floor, ceiling, inner wall, doors, and windows should be constructed.
The air conditioning system should have been put into operation.
The power supply system and indoor lighting should be constructed and put into operation.
The grounding system should have been constructed, and the grounding resistance should comply with the provisions of the design documents.

After the integrated control system is installed in place, it should meet the power supply conditions, temperature, and humidity required by the product, and the indoor environment should be kept clean.
Measures to prevent static electricity should be taken during the inspection, installation, and testing of the plug-ins.

VI. Instrument Power Supply Equipment
Before installing the power supply equipment, its appearance and technical performance should be inspected and should meet the following requirements:

The contacts of relays, contactors, and switches should be in close and reliable contact, operate flexibly, and have no corrosion or damage.
The fasteners and terminal blocks for fixing and wiring should be intact and free of dirt and corrosion.
The sealing gaskets and stuffing boxes of explosion-proof electrical equipment and accessories should be complete and sealed.
The electrical insulation performance of the equipment, the output voltage value, and the capacity of the fuse should comply with the provisions of the design documents.
The accessories of the equipment should be complete.

The specification, model, and installation location of the on-site instrument power supply box should comply with the provisions of the design documents. The equipment should not be installed in locations with high temperature, humidity, a lot of dust, explosion and fire hazards, corrosive effects, vibration, or interference with nearby instruments.
The height from the center of the on-site instrument power supply box to the operation ground should preferably be 1.20m - 1.50m. When installed in rows, it should be neatly arranged and aesthetically pleasing.
The installation of the power supply equipment should be firm, neat, and aesthetically pleasing. The equipment tag number, terminal label, purpose identification, operation identification, etc. should be complete.
When inspecting, cleaning, or installing the power supply equipment, the insulation, internal wiring, and contact parts of the equipment should not be damaged. The sealed adjustable parts on the equipment should not be unsealed. When unsealing is necessary, it should be resealed after unsealing and records should be made.
For the power supply equipment and power distribution lines installed in the panel cabinet, the electrical clearance and creepage distance between two live conductors and between a live conductor and a bare non-live conductor should comply with the following provisions:

For circuits with a rated voltage not greater than 60V, the electrical clearance and creepage distance should not be less than 3mm.
For circuits with a rated voltage greater than 60V and not greater than 300V, the electrical clearance should not be less than 5mm, and the creepage distance should not be less than 6mm.
For circuits with a rated voltage greater than 300V and not greater than 500V, the electrical clearance should not be less than 8mm, and the creepage distance should not be less than 10mm.

The terminals for strong and weak electricity should be arranged separately.
The metal power supply box should have an obvious grounding mark, and the grounding wire connection should be firm and reliable.
Before the power supply system is powered on, all the switches in the system should be in the off position, and the capacity of the fuse should be checked. During the installation and testing of the instrument project, the power-on and power-off status of all power supply switches and instruments should have a display or warning mark.