Inline and offline measurements refer to two different types of measurements. Inline Measurements are commonly referred to as automatic measurements made during a process . Offline measurements, on the other hand, are often referred to as manual measurements. The difference between the two occurs during the measurement process (line). If the measurements are included in the line then the process is considered “inline”. If it’s separate from the line then it’s considered “offline”. For off line measurements products are removed from production , inspected and returned to production ,discarded or saved as inspection samples
An Inline Measurement suggests that instruments or sensors are situated in a flow-through system. An excellent example would be a sensor attached to a manufacturing line that continually monitors the products that pass underneath. While scanning, the system should be able to ascertain the following information:
- Able to register the shapes and dimensions when judging the acceptability of a product.
- Able to perform measurements when a product passes underneath the sensor.
- Able to make a proper judgment when determining the acceptability.
- Output of NG judgment when a product has not been accepted
Inline measurement that occurs without the skill of an operator can be repeated for a large amount of products. When humans are thrown into the mix the question of skill always becomes an issue. However, when the process becomes automated there are less chances that mistakes will be made. Furthermore, consistent automated monitoring helps to identify when unacceptable products appear. This helps when tracking traceability.
In the production world work conditions can be quite demanding. Measurement results play a central role. Precision is key. Finding undesirable products on a line can only work if the tolerance testing during the production process is precise enough to reliably sort out all of the products that deemed to fall under tolerance levels.
Inline systems should be accurate no matter what type of work environment it’s in. For example, an inline measurement should be precise even if a temperature drift were to occur. Temperature drift can be caused by the surrounding temperature itself, such as the temperature in the warehouse where the inline system is located, or by the board itself. To ensure that temperature drift is not an issue, it would be a good idea to only use high quality components on your system. Also, you should pay close attention to the layout of the board. For example, components that are known to heat up while in use should be placed in an area where they will not heat up the other components of the system unnecessarily.
Also keep in mind that a good inline system can maintain its precision through interference resistance. All types of interferences can occur in the workplace:
- Mechanical – shock, vibration
- Climatic – chemicals, oil, lubricants, water, temperature, humidity
- Electromagnetic – short-circuits, ground loops, EMC radiation, overvoltage, current peaks
Ultimately, when using inline measurement, precision through automation is key no matter the conditions of the workplace.
Offline measurement relies completely on the human element. Offline measurement occurs when a measurement is performed by manually handling the measurement system in order to attain measurements for any given point or object.
Where Inline Measurement relies upon the automation and precision of machines, Offline Measurement relies upon the skill of an operator. Measurements can vary depending upon the skill of the operator. Due to the human element, offline measurements are typically not as precise as inline measurements (once again this depends upon the skill of the operator). Furthermore, due to the fact that constant monitoring is not performed, it can be quite difficult to track when unacceptable products began to appear due to a lack of statistical data. Establishing a consistent schedule of accurate measurements is considered to be an important factor in discovering stable test results.