Why an instrument datasheet is important

Find out who benefits from a datasheet.

 3 October 2019

What is a datasheet?

A datasheet or spec sheet is a document that specifies the technical characteristics of a piece of equipment. It is a summary of all properties of the equipment, the process data and environmental conditions of the location where the device will be installed, and the necessary certificates to comply with local legislation.

What’s the importance of an instrument datasheet?

An instrument datasheet is generated by an instrument engineer during the detailed engineering phase of a project. It is a document that contains plenty of information that may concern several other disciplines such as designers, automation engineers, purchasers, vendors, and maintenance technicians. The importance of an instrument datasheet lies in the fact that so many people use this information during the different design phases of a project and possibly also at a later stage for maintenance.

What follows is an overview of the different people who benefit from a well-prepared and detailed specification sheet.

Benefits for the mechanical designer

The mechanical or piping designer needs to draw the in-line instruments, such as valves or flow meters, on the piping drawing. Instruments that are not in-line are mounted on nozzles, flanged or threaded. To make these drawings, the piping designer needs the following information from the datasheet:

• Face-to-face dimensions of all in-line instruments.
• Size, class, and type of flanges or screw-threads for instruments mounted on nozzles.
• The 3D-dimensions of the instruments so that enough space can be provided for the device.
• The insertion length for each instrument that is inserted into the pipe.

Benefits for the instrument designer

The instrument or E&I designer needs to wire each instrument and should, therefore, receive the manufacturer’s wiring diagrams. He also needs to make the hook-up drawings to show how the instrument should be mounted and/or tubed. For this reason, he needs the following information from the datasheet:

• Power supply and power consumption of the instrument.
• The wiring system, two-wire or four-wire, for analog instruments. Four-wire systems are powered by an external source.
• The contact arrangement of a switch for discrete instruments, e.g. SPST or SPDT.
• The thread size and type of the in/out ports for tubed instruments.
• The possible use of a manifold and/or a mounting bracket supplied by the vendor.

Benefits for the automation engineer

The automation engineer writes the program for the PLC or DCS and designs the user interface for the HMI screens. Various data from the datasheet can be useful to him, such as:

• The calibrated range of the analog signals to configure the control system’s input channel.
• The units of the measurements displayed on the HMI screen.
• The type of bus and the protocol for communication between the instrument and the PLC or DCS.

Benefits for the purchaser

The purchaser is charged with the task to find the instrument on the market. His benefits from a datasheet are the following:

• Since he is not so well versed in technical jargon, it is easier to just refer to the datasheet.
• Sending an instrument specification datasheet to multiple vendors creates competition between them and this will provide him with the best price or the best value for money.

Benefits for the vendor

The vendor chooses the appropriate instrument from his catalog and sends a quotation to the purchaser. All he needs is:

• To receive a concise and well-arranged document that makes it quickly clear what the customer wants.
• Every vendor to receive the same information to be on equal footing with his competitors. This ensures fair competition.

Benefits for the maintenance technician

The service technician must maintain the device. This means that the device must be regularly calibrated or replaced by another device in the event of an irreparable defect. He can use the datasheet:

• To find the calibrated range and the measurement units.
• To purchase a new instrument in case of a total loss of the installed device.

And last but not least:

Benefits for the instrument engineer

Using a datasheet for purchasing an instrument or a piece of equipment has a number of advantages for the instrument engineer as well:

• Completing the datasheet makes you think about what is needed for your application. It should be a process that leads to only listing the minimum requirements for a device. Specifying too much may cost you more money.
• Using a generic datasheet template made for this kind of equipment makes it almost impossible to overlook something. With all possible property descriptions already mentioned on the datasheet template, you just have to go through them one by one and enter what you need next to each property description.
• A datasheet will give you a clear overview of your application needs and all of the properties and technical specifications of the equipment.
• By asking the supplier to complete the datasheet, it becomes possible to easily compare equipment proposed by different suppliers.

Which devices justify the use of a datasheet for purchasing?

In general, you could say that any instrument with a large set of parameters to be specified needs a datasheet to purchase it and that simple instruments with only a few parameters could do without a datasheet.

In practice, however, all instruments, from simple gauges to complex analyzers, have a large set of parameters. Think about the many process parameters, the materials of construction, process connections, power requirements, measurement range, output signals, setpoint(s), area classification… Enough information to fill one or more pages of a datasheet.

Because of the complexity of an instrument, I would recommend to always use a datasheet for the purchase of a device.

The lifespan of a datasheet

The datasheet will prove valuable as long as the purchasing process is ongoing. You can make use of it during the evaluation of tenders so you can easily check whether the supplier is offering the right material. When you have finally made your choice, you can send the datasheet as an attachment to the order.

Once the material has been delivered, you probably won’t need the datasheet any longer except if you want to buy a similar instrument later on.

Some companies are using the datasheets for maintenance. In this case, they will need to keep the datasheet updated every time the calibrated range has been changed or the instrument has been replaced by another one.

Instrument datasheet templates

Drawing up a comprehensive datasheet is time-consuming. You will have to make sure you do not forget to mention any attributes, that you provide sufficient space for the supplier to fill in something, and last but not least, you must use the correct technical terms, otherwise, misunderstandings will occur.

You can do all that by yourself and spent some hours behind your computer, or you could just take a look at this collection of datasheet templates and see if you can use one of them. There are datasheet templates for pressure gauges, pressure transmitters, pressure switches, thermometers, RTD temperature transmitters, level transmitters, … and many more will be available in the future.

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