ISA 20

These forms are intended to assist the specification writer to present the basic information. In this sense they are “short-form” specifications or “check sheets” and may not include all necessary engineering data or definitions of application requirements. While the types of instruments described by these forms are more common to the process industries the forms should also prove useful in other areas if special requirements are defined elsewhere.

Some forms consist of a primary sheet and a secondary (tabulation) sheet. The primary sheet may be used by itself to specify a single instrument or to specify general requirements for a series of similar instruments which are then tabulated on the secondary sheet.

The heading used on all forms is designed to permit the user to add company name, plant location, trade mark, or specific project data.

The specification forms included in this standard are intended to cover the most commonly used instruments. The list is not a complete catalog of instruments and control valves available. It is intended that new forms shall be added with each general revision of this standard.

An instruction sheet is provided for each form to explain the terms used and the intended procedure. The instructions are keyed to the form by reference to the line numbers. The Committee has minimized dependence on the instruction sheet since the forms are frequently reprinted and used without the instructions. The explanation is omitted where the meaning is felt to be obvious.

Instrument specifications may be prepared by the use of Automatic Data Processing (ADP) techniques. The format of such specifications may be modified in order to be compatible with ADP machine capabilities. However, general consistency with this Standard shall be retained.

Purpose

The purpose of this standard is to promote uniformity in instrument specifications, both in content and form. Because of the complexity of present day instruments and controls it is desirable to have some type of specification form to list pertinent details for use by all interested parties. General use of these forms by users and manufacturers offers many advantages, as listed below:

1) Assists in preparation of complete specification by listing and providing space for all principal descriptive options.

2) Promotes uniform terminology*.

3) Facilitates quoting, purchasing, receiving, accounting and ordering procedures by uniform display of information.

4) Provides a useful permanent record and means for checking the installation.

5) Improves efficiency from the initial concept to the final installation.

*Where applicable, the terminology used is in accordance with American National Standards C85.1-1963, “Terminology for Automatic Control,” sponsored by the American Society of Mechanical Engineers.