Instrument Loop Check Sheet Template
A complete loop check record for analog input loops: mechanical and wiring pre checks, a 5 point injection test compared with the DCS or PLC display, and alarm and trip verification.
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- How to Use sheet with steps
- Template sheet, blank and ready
- Example sheet, filled in
- 50 built in formulas
- A4 portrait print setup
- Works in Excel, Google Sheets and LibreOffice
Preview of the Filled Example
This is the Example sheet from the download, so you can see exactly how the completed instrument loop check sheet looks.
Pre checks
| No | Check item | Status | Remarks |
|---|---|---|---|
| 1 | Instrument installed as per hook up drawing and tag plate fitted | OK | |
| 2 | Process connection, impulse lines and manifold leak tested | OK | |
| 3 | Cable glanded, terminated and ferruled as per termination schedule | OK | |
| 4 | Insulation resistance of loop cable checked (≥ 100 MΩ at 500 V DC, instrument disconnected) | OK | |
| 5 | Continuity and polarity checked field to marshalling to I/O card | OK | |
| 6 | Shield earthed at one end only (control room side) | OK | |
| 7 | IS barrier / isolator type matches the loop drawing (if IS loop) | NA | Non IS loop |
| 8 | Instrument range and configuration match the data sheet | OK |
Loop test: signal injected at the field, reading checked on DCS / PLC display
| Injected (%) | Injected (mA) | Expected reading | DCS / PLC reading | Error (% span) | Result | Remarks |
|---|---|---|---|---|---|---|
| 0 | 4.00 | 0.00 | 0.00 | 0.00 | PASS | |
| 25 | 8.00 | 4.00 | 4.01 | 0.06 | PASS | |
| 50 | 12.00 | 8.00 | 8.02 | 0.12 | PASS | |
| 75 | 16.00 | 12.00 | 12.01 | 0.06 | PASS | |
| 100 | 20.00 | 16.00 | 16.00 | 0.00 | PASS |
Alarm and trip check
| Alarm | Set point | Activated at | Deviation | Shown on HMI and logged? | Remarks |
|---|---|---|---|---|---|
| L | 4.00 | 4.00 | 0.00 | Yes | |
| H | 13.00 | 13.00 | 0.00 | Yes | |
| HH | 14.50 | 14.50 | 0.00 | Yes | Trips boiler feed via SIS (tested separately) |
About the Instrument Loop Check Sheet
A loop check proves that a field instrument, its cable, junction box, marshalling, I/O card and the DCS or PLC configuration all work together before the plant starts up. A complete loop check sheet is a key commissioning record: it is signed by the contractor, the client and often the system vendor, and is part of the mechanical completion and handover dossier.
How to fill in this template
- Fill the loop details from the loop drawing, I/O list and data sheet. Range and tolerance drive the test calculations.
- Complete the pre checks before powering the loop. Do not inject signals into a loop with incomplete wiring checks.
- Disconnect the transmitter (or use it in loop test mode) and inject 4, 8, 12, 16 and 20 mA at the field end; record what the DCS or PLC displays.
- Simulate each alarm and trip point and confirm the alarm appears on the HMI and in the event log.
- All parties sign the sheet. Attach it to the loop folder for handover.
What the formulas do
- Injected mA = 4 + 16 × % ÷ 100.
- Expected reading = LRV + span × % ÷ 100.
- Error = (DCS reading − expected) ÷ span × 100; PASS within the loop tolerance.
- Deviation = alarm activation value − set point.
Related tools
Frequently Asked Questions
What is the difference between a cold loop and a hot loop check?
A cold loop checks wiring continuity and insulation without power. A hot loop (this sheet) injects real signals with the system powered and checks the reading, ranging and alarms end to end.
Where should the signal be injected?
At the field end, as close to the instrument as possible, so the whole loop including the cable and junction box is proven.
What tolerance is acceptable for a loop check?
Typically ± 0.5 % of span, covering the I/O card accuracy and the injection source.
Learn more on the blog
Instrument loop checking: a complete step by step procedure
A practical guide on instrumentationblog.in that explains the procedure behind this template and how engineers apply it on real plants.
Read Full Article