Requirements specification in machine building, with an example.
A requirements specification is quick to fill and hard to do well. This page shows what belongs in one for machine and plant building, using a fully worked example. And it shows what happens to the document once the order is in and project management takes over.
A requirements specification (German: Lastenheft) describes what the customer requires of a machine or plant: performance, product, interfaces, installation, safety, documentation, acceptance and dates. It states what is required, not how. The how is the supplier's functional specification (Pflichtenheft). In special machine building, customer and sales often write it together and revise it several times before the order.
What a requirements specification is in machine building.
The customer's description of what they need. Who writes it depends on what is being built.
- 08.07.2026Rev. 1.1
Acceptance scope agreed
- 02.09.2026Rev. 1.2
Restructured
- 21.10.2026Rev. 2.0
Released for order
- 15.01.2027Purchase order
Handover to project management
- 19.09.2026 · Sales emailCycle time of 10.5 s confirmed
- 24.09.2026 · Sales meeting noteVariant V4 promised
- 08.07.2026 · Specification Rev. 1.1Acceptance scope, dropped in Rev. 1.2
The customer usually writes the specification alone and sends it to several suppliers. It records what the machine must achieve and under which conditions it will run. The suppliers reply with a quotation, and the document itself rarely changes along the way.
The specification is a shared document. The customer brings a first draft, sales asks questions, does the sums and proposes alternatives. With the purchase order, the latest revision becomes part of the contract, not what was agreed along the way in emails and notes.
What belongs in a requirements specification.
Fourteen chapters for a machine or plant. What matters is that every value can be checked at acceptance.
- 1Change log
- 2Background and goal
- 3Scope and boundaries
- 4Parts and variants
- 5Process sequence
- 6Performance requirements
- 7Quality requirements
- 8Technical requirements
- 9Controls, operation, data
- 10Safety and standards
- 11Documentation
- 12Acceptance
- 13Dates
- 14Service, training, warranty
The structure varies from industry to industry, the core does not. For a machine or plant there are fourteen points: change log, background and goal, scope and boundaries, parts and variants, process sequence, performance requirements, quality requirements, technical requirements, controls and data, safety and standards, documentation, acceptance, dates, and service and warranty.
What matters is less the completeness of the headings than whether the values can be checked. "High availability" cannot be demonstrated at acceptance, "technical availability ≥ 95 % to VDI 3423 over ten production days" can. Every requirement therefore gets an ID, a value and the method of proof used at acceptance. “Must” is an acceptance criterion, “should” is a target value.
A worked requirements specification.
The specification below describes an assembly and test cell for thermostatic valve bodies. Companies, people and values are invented, but the numbers add up: cycle time, volume and shift pattern fit together. The notes in the margin show what was promised in the quotation phase and is missing from the document.
Requirements specification
Assembly and test cell for thermostatic valve bodies
Project MPZ-TV2, Nordtal Armaturen GmbH, Wels plant
Fictional example: all companies, people and values are invented.
- Document no.
- NA-LH-2026-014
- Revision / date
- 2.0 / 21.10.2026
- Status
- Released for order
- Customer
- Nordtal Armaturen GmbH, Wels plant
- Supplier
- Hollmann Automation GmbH, Linz
- Reference
- Quotation AN-24-0871 Rev. C of 30.09.2026
- Supplier contact
- Thomas Berger, Sales
| Name / department | Date | Signature | |
|---|---|---|---|
| Prepared | Sabine Moser, Production Planning | 21.10.2026 | signed Moser |
| Checked | Petra Lindner, Quality Assurance | 21.10.2026 | signed Lindner |
| Released | Martin Gruber, Purchasing | 21.10.2026 | signed Gruber |
This specification becomes part of the purchase order. Side agreements apply only if they are agreed in writing and incorporated into this document.
Appendices: A part drawings, B installation layout, C customer component list, D limit sample catalogue
What the specification does not say
Three commitments from the quotation phase are not in Rev. 2.0. They are in an email, a meeting note and an older revision. With the purchase order, project management takes over Rev. 2.0 only.
What the specification does not say
Three commitments from the quotation phase are not in Rev. 2.0. They are in an email, a meeting note and an older revision. With the purchase order, project management takes over Rev. 2.0 only.
1Change log
| Rev. | Date | Change | Author |
|---|---|---|---|
| 2.0 | 21.10.2026 | Released for order; section 9 MES interface added; editorial changes | Moser |
| 1.23 | 02.09.2026 | Restructured; cycle time and traceability specified in more detail | Moser |
| 1.1 | 08.07.2026 | Variant list, layout and acceptance added after clarification meeting with supplier | Moser, Lindner |
| 1.0 | 12.06.2026 | First issue | Moser |
2Background and goal
The valve bodies are currently assembled at three manual workstations and leak tested on a separate test stand. Output and traceability are no longer sufficient for the planned volumes.
The goal is a linked, semi-automatic cell that handles assembly, leak testing and marking in one cycle and reports every part with its test values to the manufacturing execution system (MES).
3Scope and boundaries
3.1 Supplier scope
Design, manufacturing, assembly, controls and software, commissioning, CE marking, documentation, training, factory and site acceptance.
3.2 Customer supplies
Parts and limit samples for acceptance, power and compressed air up to the connection point, network connection, hall floor, MES counterpart.
3.3 Not in scope
Packaging after the cell, transport containers, building work.
4Parts and variants
| Variant | Part no. | Design | Connection | Share 2027 |
|---|---|---|---|---|
| V1 | 4410-10D | Straight | DN10 (3/8") | 20 % |
| V2 | 4410-15D | Straight | DN15 (1/2") | 55 % |
| V32 | 4410-15E | Angle | DN15 (1/2") | 25 % |
Components per valve: valve body (brass CW617N), EPDM O-ring 17 × 2, valve insert (pre-assembled, supplied by the customer). Drawings and tolerances see appendix A.
5Process sequence
Rotary indexing table with 8 stations, one operator at the loading station.
| Station | Operation | Remark |
|---|---|---|
| S1 | Load valve body | manual, guarded by light curtain |
| S2 | Check variant and orientation | camera |
| S3 | Separate, grease and fit O-ring | |
| S4 | Feed and screw in valve insert | torque and angle monitored |
| S5 | Leak test | pressure decay, air |
| S6 | Laser and verify DataMatrix | |
| S7 | Unload OK parts, reject NOK parts | NOK into locked box |
| S8 | Check fixture is empty |
6Performance requirements
Every requirement has an ID, a value and a method of proof. “Must” is an acceptance criterion. “Should” is a target value; the supplier justifies deviations in writing.
| ID | Requirement | Value | Proof | Priority |
|---|---|---|---|---|
| L-011 | Technical cycle time (machine cycle, mean over 100 parts, without operator waiting time) | ≤ 12.0 s | Time measurement at FAT and SAT | Must |
| L-021 | Annual demand, design basis | 780,000 pcs (2027) | 2 shifts × 7.5 h × 220 days, OEE 85 % | Info |
| L-03 | Technical availability (downtime caused by the cell) | ≥ 95 % | Performance run at SAT | Must |
| L-04 | Changeover time between variants, tool-free, coded fixture inserts | ≤ 15 min | Demonstration at FAT | Must |
| L-05 | Autonomy of O-ring and valve insert feeders | ≥ 30 min | Measurement at FAT | Should |
| L-06 | Restart after emergency stop until production | ≤ 2 min | Demonstration at FAT | Should |
7Quality requirements
| ID | Requirement | Value | Proof | Priority |
|---|---|---|---|---|
| Q-012 | Tightening torque valve insert V1 to V3, angle window monitored | 25 Nm ± 2 Nm | Screwing data per part | Must |
| Q-02 | Leak tightness, pressure decay with air, test pressure 6 bar (gauge) | ≤ 0.5 cm³/min | OK and NOK master parts | Must |
| Q-03 | False rejects (OK parts rated NOK) | ≤ 0.5 % | Evaluation of performance run | Must |
| Q-04 | Slip (NOK parts rated OK) | 0 of 20 | 20 NOK master parts | Must |
| Q-05 | DataMatrix marking, code quality to ISO/IEC TR 29158 | at least grade B | Verification in S6 | Must |
| Q-06 | Record per part: serial number, time stamp, variant, torque and angle, leak rate, result | 100 % of parts | Sample of 50 records in the MES | Must |
8Technical requirements
| Topic | Requirement |
|---|---|
| Footprint | max. 4.5 × 3.5 m, height max. 2.6 m, position as per layout appendix B |
| Electrical supply | 400 V 3/N/PE, 50 Hz, fusing max. 32 A |
| Compressed air | 6 bar, oil-free, purity ISO 8573-1 class [1:4:1]; state consumption in the quotation |
| Noise | Sound pressure level at the operator station ≤ 75 dB(A) |
| Ergonomics | Loading height 950 mm ± 50 mm, loading without bending or stretching |
| Guarding | RAL 7035, polycarbonate windows, doors with guard locking |
| Purchased parts | as per customer component list (appendix C); deviations only after written approval |
9Controls, operation, data
| Topic | Requirement |
|---|---|
| Control | Siemens S7-1500 with safety CPU (F-CPU); agree software version at order |
| Operation | 15" operator panel, German and English, user levels operator, setter, maintenance |
| MES connection | OPC UA, record per part as per Q-06; local buffer ≥ 30 days during network outage |
| Remote service | only via the customer's VPN access |
| Source code | PLC and operator panel program unencrypted to the customer |
10Safety and standards
| Topic | Requirement |
|---|---|
| CE marking | under Machinery Regulation (EU) 2023/1230, applicable from 20.01.2027; delivery takes place afterwards |
| Risk assessment | to EN ISO 12100 by the supplier, handed over to the customer |
| Safety functions | to EN ISO 13849-1; required performance level per function from the risk assessment |
| Electrical equipment, guards | EN 60204-1; fixed guards to EN ISO 14120 |
11Documentation
In German, as PDF and in the original formats. Draft at factory acceptance, final version at site acceptance.
- Operating instructions, maintenance plan
- Risk assessment, EU declaration of conformity
- Circuit diagrams (EPLAN) and pneumatic diagrams
- Parts lists, spare and wear parts list (recommendation for 2 years)
- 3D models (STEP) of the customer-specific parts
12Acceptance
12.1 Factory acceptance (FAT) at the supplier
- Function test of all variants V1 to V3
- Performance run of 300 parts variant V2 with cycle time measurement (L-01)
- Master part test for leak tightness (Q-02, Q-04)
- Changeover demonstration (L-04) and test of all safety functions
- Documentation in draft
Release for shipment only without open “must” items.
12.2 Site acceptance (SAT) at the customer3
The final payment is made after the signed site acceptance.
13Dates
| Milestone | Date |
|---|---|
| Purchase order | 15.01.2027 |
| Design release by customer | CW 10/2027 |
| Factory acceptance (FAT) | CW 24/2027 |
| Delivery and installation | CW 27/2027 |
| Site acceptance (SAT) | CW 30/2027 |
| Start of series production | 01.09.2027 |
14Service, training, warranty
| Topic | Requirement |
|---|---|
| Warranty | 24 months from signed site acceptance |
| Response time for faults | by phone 4 h, on site 48 h (working days) |
| Training | Operators 2 × 4 h, maintenance 2 days, at the customer |
| Spare parts | Availability for 10 years from delivery |
Timeline
- 08.07.2026Specification Rev. 1.1Full acceptance scope agreed3
- 02.09.2026Specification Rev. 1.2Restructured, acceptance scope dropped without a note3
- 19.09.2026Sales emailCycle time of 10.5 s confirmed1
- 24.09.2026Sales meeting noteVariant V4 promised2
- 30.09.2026Quotation AN-24-0871 Rev. CExtra cost for second test station included1
- 05.10.2026Sales email“Acceptance as discussed”3
- 21.10.2026Specification Rev. 2.0Released for order, without commitments 1 to 3
- 15.01.2027Purchase orderHandover to project management
What becomes of the specification after the order.
Until the order, the specification belongs to sales. After that, project management mainly gets one thing: the latest version.
Sales agreed it with the customer, know every version and remember what was said about it on the phone and in meetings. That knowledge does not automatically move with the order.
Earlier versions sit somewhere in the project folder. The emails with the customer sit in the sales inbox, the meeting notes in a notebook or a file nobody opens again. All of it is rarely read, because nobody has time to work through three months of negotiation. Yet that is exactly where the commitments are that the document lacks.
In the example above there are three: a cycle time of 10.5 seconds promised by email, a variant V4 with a higher tightening torque from a meeting note, and an acceptance scope with capability studies that disappeared from the specification without a note during a restructuring. None of them is in the revision that was ordered. All three cost money if they only surface at acceptance.
There are two ways to catch this. Organisationally, with a handover meeting in which sales names every gap between document and agreement. And technically, by making the specification, its versions, the emails and the minutes searchable in one place. KoAssist reads these documents and answers a question such as "What did we promise the customer on cycle time?" with the place where it is written: document, email or note.
Requirements and functional specification.
The requirements specification says what is required. The functional specification says how the supplier delivers it.
| Requirements specification | Functional specification | |
|---|---|---|
| Written by | The customer, often with the supplier's sales team | The supplier |
| Content | What is required | How it is delivered |
| When | Before the order | After the order, approved by the customer |
| In the example | Technical cycle time ≤ 12.0 s | Rotary indexing table with 8 stations, cycle time calculation |
The functional specification covers the cell concept, stations, components and cycle time calculation. In machine building the supplier writes it after the order, the customer approves it, and only then does detailed design begin. Where the two documents diverge, what was agreed in the contract usually applies. That is why a line-by-line comparison pays off.
The template to download.
The same structure as the example, blank and ready to fill in.
Requirements specification template for machines and plants
- Cover page with document data and release
- Change log with the affected section
- 14 chapters, every requirement with value, proof and priority
- Appendix for commitments outside the specification
Word file (.docx), 30 KB, five pages. The template is in German, with the same structure as the example above. Free.
Every requirement has an ID, a value, a method of proof and a priority, plus filling notes per chapter. At the end is an appendix for everything promised in emails, meetings or older revisions. It goes to project management with the purchase order.
Frequently asked questions
The answers refer to machines and plants in special machine and plant building.
What is the difference between a requirements specification and a functional specification?
The requirements specification describes what the customer requires. The functional specification describes how the supplier meets those requirements. In machine building the functional specification is written after the order and approved by the customer.
Who writes the requirements specification?
Formally the customer. In special machine and plant building it is often a joint effort, though: the customer supplies a first draft and the supplier's sales team agrees it with them up to the order.
Is the requirements specification part of the contract?
Usually yes, in the version named in the order. Agreements that only exist in emails or meeting notes are therefore a risk: depending on the contract they apply or they do not, and the argument about it often only starts at acceptance.
How long is a requirements specification for a special machine?
For a cell the size of the example, 10 to 30 pages are typical, considerably more with appendices such as drawings, company standards and layouts. More important than length is that every requirement is numbered and can be checked at acceptance.
What happens to changes after the order?
They belong in a new version with a change log, and if they affect price or schedule, in a change order. Changes agreed only verbally or by email are the easiest to lose when the project passes to project management.
Is there a standard for requirements specifications?
The German terms Lastenheft and Pflichtenheft are defined in DIN 69901-5, and VDI 2519 describes the procedure and contents for automation projects. No standard prescribes a binding structure.
