First of all, be clear on what you want to achieve, or which questions you are looking to answer. As an example, you might want to learn if the process remains stable and predictable when you change a raw material batch or supplier, or change to a different upstream feed tank, or change production shift …? Be clear that your sampling plan convinces you the question/s of interest can be answered.
I learnt from Donald Wheeler many years ago that “so long as you have signals you have enough data” … if you have signals (on your control chart) you have detected process changes that are worthy of investigation – investigate, learn what you can, and take action.
If your signals come from a chart looking like Figure 1 above you are probably sampling too fast. Use your knowledge of the process to “best guess” how quickly your process can change … (ask the shop floor what they think and get them involved). If you think, for example, that meaningful process changes cannot occur at a faster rate than every 10 minutes then don’t sample much quicker than this.
As Doug writes above, challenge your current sampling plan and adapt it to correct the weak points in it that you identify. You may not find a weak point today, but you may tomorrow. When you find the weak point adapt things accordingly.
Hi Robert, good question…
First of all, be clear on what you want to achieve, or which questions you are looking to answer. As an example, you might want to learn if the process remains stable and predictable when you change a raw material batch or supplier, or change to a different upstream feed tank, or change production shift …? Be clear that your sampling plan convinces you the question/s of interest can be answered.
I learnt from Donald Wheeler many years ago that “so long as you have signals you have enough data” … if you have signals (on your control chart) you have detected process changes that are worthy of investigation – investigate, learn what you can, and take action.
If your signals come from a chart looking like Figure 1 above you are probably sampling too fast. Use your knowledge of the process to “best guess” how quickly your process can change … (ask the shop floor what they think and get them involved). If you think, for example, that meaningful process changes cannot occur at a faster rate than every 10 minutes then don’t sample much quicker than this.
As Doug writes above, challenge your current sampling plan and adapt it to correct the weak points in it that you identify. You may not find a weak point today, but you may tomorrow. When you find the weak point adapt things accordingly.