An instrument specification is a high-level document that provides a general overview of the instrument and its capabilities, whereas an instrument datasheet is a detailed document that provides specific information about the instrument's design, materials, and operating parameters. An instrument specification sheet is a document that gives the technical details of an instrument or device.

A datasheet will tell you everything you need to know about the instrument’s features and technical specifications. The specification sheet contains considerably more detailed information that is tailored to the application.

A project will be successful if the selected instruments are strictly as per the process requirements. It is essential that the selected instrument must be as close as possible to the requirement of the plant as regards to span, environmental conditions, enclosure class, accuracy, output, process connection, material of construction, and regulatory requirements. The instrumentation specification sheet contributes to enhanced process monitoring and plant security. The instrument data sheet is created by the instrumentation engineer. Once we create a specification sheet for a particular instrument, the same is delivered along with a request to many vendors. When giving their estimates, based on requirements, vendors will list a variety of models and manufacturers. The job of the instrument engineer is to look at each quote and choose the one that meets technical standards and process requirements.

After technical and economic considerations, the instrument is purchased. The vendor sends documents and drawings after getting the purchase order. Using vendor data, an instrument’s specification sheet can be changed to reflect “as-built” details.

Specification sheets and vendor data are saved in a library or document control room for construction, operation, and maintenance to be used for further reference. Based on your work place viz. either working with a contractor, or with a consultant, or even with a client the importance of each parameter changes and in some cases some data points becomes more relevant. These sheets are also used while inspection, installation, and commissioning.

Specification sheet lists general information about the instrument, such as its

• Tag number
• Product name and Model Number: To be included after market survey
• Service description and its intended use: Like steam/water/pulp etc.
• Location (line number or equipment number): To be gathered from P&I
• P&ID number or drawing number: With latest revision
• Detailed technical specifications, such as measurement range, accuracy, resolution, and precision
• Operating conditions, such as temperature, humidity, and pressure range
• Electrical requirements, such as power input, voltage, and current
• Material of construction and enclosure material
• Performance characteristics, such as accuracy, linearity, response time, stability, and sensitivity
• Physical dimensions and weight of the instrument
• Safety features and precautions, Hazardous certification if any (for an electrical device)
• Maintenance and cleaning instructions: Detailed in maintenance manual
• Calibration and repair information
• Warranty and support information
• Accessories needed, etc.

Each type of instrument, such as a transmitter, switch, gauge, I/P converter, Variable Frequency Drive (VFD), Solenoid or control valve, may have different information in its data sheet.