What is the difference between panel-mounted instruments, instruments installed behind a panel, and rack-mounted instruments? ?

Panel-mounted instruments involve making holes in the dashboard, inserting the instruments into those holes, and securing them with clamps at the back of the panel； Mounted instruments are fixed with screws on brackets placed behind panels or in cabinets. Gauge dial instruments that require indication, recording, and operation ； Instrument racks for instruments that require no indication, recording, or operation.

How do panel-mounted instruments achieve indication, recording, and control? Is there a PLC or a dry contact circuit?

The term ‘instrument’ mentioned here refers to conventional instruments; DCS, PLC, etc. do not fall under conventional instruments； In automation projects that use conventional instruments, they can be divided into primary instruments and secondary instruments. Primary instruments are those located at the site, including transmitters, sensors, control valves, etc., while secondary instruments include those used for indication, alarm signaling, recording, control, calculation, etc. Secondary instruments are divided into panel-mounted instruments and rack-mounted instruments. Instruments for indication, alarm, recording, control, etc. are panel-mounted instruments; holes need to be made in the dashboard before the instruments are inserted, with their displays facing the dashboard surface. Rack-mounted instruments are installed on the framework behind the dashboard or on instrument racks behind it; these are usually instruments used for conversion, calculation, and similar functions. Today, control devices based on computer and communication technologies such as DCS and PLC are widely used; indication, alarm, and recording functions are carried out at the operator station, while control and calculation tasks take place internally, which is why secondary instruments are rarely used.