Introduction
The document discusses the considerations for calibrating field instruments either in the field or in a workshop. While field calibration is often preferred, workshop calibration can be more convenient and effective in certain situations.

1. Commissioning
During the commissioning of a new plant, calibrating equipment in a workshop is efficient as the process equipment is not yet installed. This allows for faster calibration of transmitters before installation, saving time and aligning with tight schedules.

2. Total Uncertainty of Calibration
Workshop calibration can reduce total uncertainty due to controlled conditions and better-performing equipment compared to portable field equipment. Consistent operating procedures in workshops also contribute to more accurate calibrations.

3. Primary Standards in a Workshop
Workshops can house higher-accuracy, non-portable calibration equipment as primary standards. This allows for in-house calibration of portable field calibrators, saving time and money by reducing the need for external recalibrations.

4. Spare Device Calibration / Rotating Spares
Calibrating spare devices in a workshop is convenient when field calibration is challenging or time-consuming. This approach allows for seamless replacement of devices in the process.

5. Safety
Workshops can be equipped with safety facilities such as isolation transformers and emergency switches, which are difficult to implement in field conditions.

6. Accreditation and Quality System
Obtaining accreditation for calibration work is easier in a workshop setting, where uncertainty can be minimized. A quality system is also more feasible in a controlled workshop environment.

7. Field Conditions vs. Workshop Conditions
Field conditions can be hazardous and challenging, requiring protective gear and suitable equipment. Workshops provide a more ergonomic and efficient environment for calibration work.

8. Efficiency, Ergonomics, Ease of Use
Workshops offer a more organized and ergonomic workspace, with equipment always ready for use, reducing the risk of lost or uncharged equipment.

Summary Comparison
Both workshop and field calibrations have their advantages. Field calibration allows for calibration of the entire measurement loop in actual process conditions, while workshop calibration offers better accuracy, safety, and efficiency. The choice between the two depends on specific circumstances, and often both methods are used complementarily.