Build an EWMA chart

Example: sealing temperature

A technician records the sealing-jaw temperature every 15 minutes. The example follows 120 readings from the same location after thermal settling.

Download the sealing-temperature example (CSV)

This is the same example used in Help. temperature_c contains temperature in °C. An earlier study supplied the reference mean of 180 °C and standard deviation of 0.60 °C. Keep the readings in collection order.

1. Create the workspace

In the sidebar, open Process control, choose EWMA Chart, and name the analysis. Select New blank worksheet and Create analysis.

2. Import the data

On Worksheet, choose Import. Select the downloaded file or paste its contents. Set the delimiter to Comma, use Decimal dot, and check First row contains column names. Preview the import, then choose Import into worksheet. Keep the rows in collection order.

3. Assign the input columns

On Inputs, choose Individuals under Subgrouping method. Assign temperature_c to Measurements, selecting it from the column picker. Leave Subgroup ID empty.

4. Set the reference and limits

Enter 0.3 in EWMA weight (λ) and 3 in Control limit multiplier (k). Under Standard deviation estimation, choose Historical standard deviation (σ). Enter 0.60 in Historical standard deviation (σ) and 180 in Historical mean (optional). These values use °C.

Choose Time varying under Control limits. Leave Apply bias correction to standard deviation estimate checked; this run uses the supplied historical standard deviation, which the bias-correction checkbox does not change.

EWMA Chart: Inputs with the example’s assignments and settings — Individual temperatures, historical reference values and time-varying EWMA limits on Inputs. View full-size image (opens in a new tab)

5. Run analysis

Choose Run analysis, then open Results.

6. Interpret results

Understand each point
Each EWMA point combines 30% of the newest temperature with 70% of the previous EWMA. It shows recent temperatures as a smoothed average, rather than showing only the current reading.
Look for a sustained change
Points 113–115 and 117–120 cross the upper limit. The weighted average has risen late in the sequence. Check the temperatures leading up to these signals as well as the flagged readings.
Smoothed temperature in °C for 120 readings. The limits widen toward their steady-state values. View full-size chart (opens in a new tab)
Check the reference
This run uses the earlier study’s mean of 180 °C and standard deviation of 0.60 °C. It does not estimate them from these readings. The time-varying limits start at 179.460–180.540 °C and gradually approach 179.244–180.756 °C.
Decide what to investigate
Review temperature and operating records leading into observations 113–120. Confirm that the earlier reference still applies to this process. A signal shows a departure from that reference; it does not identify a cause or establish whether a temperature meets product requirements.

More details: read each result section

Complete result tables use six significant digits, as in Help.

EWMA summary

This run uses the supplied historical mean of 180 °C and sigma of 0.60 °C, rather than estimating them from the example. λ = 0.3 and k = 3 control smoothing and limit width. Time-varying limits start at 179.460–180.540 °C and approach 179.244–180.756 °C.

EWMA summary · 13 rows
Statistic / setting	Value
Observations / subgroups	120
Lambda (λ)	0.3
k	3
Center line	180
Mean source	historical
Sigma	0.6
Sigma source	historical
Sigma mode	historical
Bias correction	true
Moving-range span	—
Moving-range statistic	—
Limit mode	time varying
Steady-state start	—

EWMA values and control limits

Compare each original temperature with its EWMA and time-specific limits. The EWMA is smoothed; a flagged EWMA does not imply that the original reading fails a temperature specification. Read the startup limits separately from their later limiting values.

EWMA values and control limits · 120 rows
Observation / subgroup	Label	Subgroup size	Subgroup mean	EWMA	Recursive σZ	Limit σZ	CL	LCL	UCL	Signal
1	—	1	180.69	180.207	0.18	0.18	180	179.46	180.54	false
2	—	1	180.93	180.424	0.219718	0.219718	180	179.341	180.659	false
3	—	1	180.11	180.33	0.23676	0.23676	180	179.29	180.71	false
4	—	1	180.15	180.276	0.244677	0.244677	180	179.266	180.734	false
5	—	1	180.22	180.259	0.248465	0.248465	180	179.255	180.745	false
6	—	1	180.8	180.421	0.2503	0.2503	180	179.249	180.751	false
7	—	1	180.77	180.526	0.251194	0.251194	180	179.246	180.754	false
8	—	1	179.1	180.098	0.251631	0.251631	180	179.245	180.755	false
9	—	1	179.19	179.826	0.251845	0.251845	180	179.244	180.756	false
10	—	1	180.37	179.989	0.25195	0.25195	180	179.244	180.756	false
11	—	1	180.38	180.106	0.252001	0.252001	180	179.244	180.756	false
12	—	1	180.36	180.182	0.252026	0.252026	180	179.244	180.756	false
13	—	1	178.92	179.804	0.252039	0.252039	180	179.244	180.756	false
14	—	1	179.79	179.8	0.252045	0.252045	180	179.244	180.756	false
15	—	1	180.75	180.085	0.252048	0.252048	180	179.244	180.756	false
16	—	1	179.65	179.954	0.252049	0.252049	180	179.244	180.756	false
17	—	1	180.3	180.058	0.25205	0.25205	180	179.244	180.756	false
18	—	1	179.64	179.933	0.25205	0.25205	180	179.244	180.756	false
19	—	1	180.28	180.037	0.25205	0.25205	180	179.244	180.756	false
20	—	1	179.09	179.753	0.25205	0.25205	180	179.244	180.756	false
21	—	1	180.04	179.839	0.25205	0.25205	180	179.244	180.756	false
22	—	1	179.3	179.677	0.25205	0.25205	180	179.244	180.756	false
23	—	1	179.83	179.723	0.25205	0.25205	180	179.244	180.756	false
24	—	1	180.12	179.842	0.25205	0.25205	180	179.244	180.756	false
25	—	1	180.57	180.061	0.25205	0.25205	180	179.244	180.756	false
26	—	1	180.53	180.201	0.25205	0.25205	180	179.244	180.756	false
27	—	1	180.04	180.153	0.25205	0.25205	180	179.244	180.756	false
28	—	1	181.09	180.434	0.25205	0.25205	180	179.244	180.756	false
29	—	1	179.96	180.292	0.25205	0.25205	180	179.244	180.756	false
30	—	1	179.34	180.006	0.25205	0.25205	180	179.244	180.756	false
31	—	1	179.66	179.902	0.25205	0.25205	180	179.244	180.756	false
32	—	1	180.14	179.974	0.25205	0.25205	180	179.244	180.756	false
33	—	1	180.31	180.075	0.25205	0.25205	180	179.244	180.756	false
34	—	1	178.01	179.455	0.25205	0.25205	180	179.244	180.756	false
35	—	1	179.09	179.346	0.25205	0.25205	180	179.244	180.756	false
36	—	1	180.36	179.65	0.25205	0.25205	180	179.244	180.756	false
37	—	1	179.55	179.62	0.25205	0.25205	180	179.244	180.756	false
38	—	1	179.45	179.569	0.25205	0.25205	180	179.244	180.756	false
39	—	1	180.98	179.992	0.25205	0.25205	180	179.244	180.756	false
40	—	1	180.99	180.292	0.25205	0.25205	180	179.244	180.756	false
41	—	1	180.69	180.411	0.25205	0.25205	180	179.244	180.756	false
42	—	1	178.89	179.955	0.25205	0.25205	180	179.244	180.756	false
43	—	1	179.91	179.941	0.25205	0.25205	180	179.244	180.756	false
44	—	1	179.86	179.917	0.25205	0.25205	180	179.244	180.756	false
45	—	1	180.25	180.017	0.25205	0.25205	180	179.244	180.756	false
46	—	1	181.19	180.369	0.25205	0.25205	180	179.244	180.756	false
47	—	1	180.43	180.387	0.25205	0.25205	180	179.244	180.756	false
48	—	1	180.25	180.346	0.25205	0.25205	180	179.244	180.756	false
49	—	1	179.91	180.215	0.25205	0.25205	180	179.244	180.756	false
50	—	1	180.54	180.313	0.25205	0.25205	180	179.244	180.756	false
51	—	1	178.82	179.865	0.25205	0.25205	180	179.244	180.756	false
52	—	1	179.21	179.668	0.25205	0.25205	180	179.244	180.756	false
53	—	1	178.7	179.378	0.25205	0.25205	180	179.244	180.756	false
54	—	1	179.4	179.385	0.25205	0.25205	180	179.244	180.756	false
55	—	1	179.96	179.557	0.25205	0.25205	180	179.244	180.756	false
56	—	1	180.23	179.759	0.25205	0.25205	180	179.244	180.756	false
57	—	1	180.77	180.062	0.25205	0.25205	180	179.244	180.756	false
58	—	1	179.79	179.981	0.25205	0.25205	180	179.244	180.756	false
59	—	1	180.62	180.172	0.25205	0.25205	180	179.244	180.756	false
60	—	1	179.74	180.043	0.25205	0.25205	180	179.244	180.756	false
61	—	1	181.04	180.342	0.25205	0.25205	180	179.244	180.756	false
62	—	1	179.77	180.17	0.25205	0.25205	180	179.244	180.756	false
63	—	1	180.66	180.317	0.25205	0.25205	180	179.244	180.756	false
64	—	1	179.14	179.964	0.25205	0.25205	180	179.244	180.756	false
65	—	1	180.12	180.011	0.25205	0.25205	180	179.244	180.756	false
66	—	1	179.19	179.765	0.25205	0.25205	180	179.244	180.756	false
67	—	1	179.87	179.796	0.25205	0.25205	180	179.244	180.756	false
68	—	1	180.06	179.875	0.25205	0.25205	180	179.244	180.756	false
69	—	1	180.16	179.961	0.25205	0.25205	180	179.244	180.756	false
70	—	1	180.16	180.021	0.25205	0.25205	180	179.244	180.756	false
71	—	1	181.32	180.41	0.25205	0.25205	180	179.244	180.756	false
72	—	1	179.32	180.083	0.25205	0.25205	180	179.244	180.756	false
73	—	1	180.61	180.241	0.25205	0.25205	180	179.244	180.756	false
74	—	1	180.4	180.289	0.25205	0.25205	180	179.244	180.756	false
75	—	1	179.99	180.199	0.25205	0.25205	180	179.244	180.756	false
76	—	1	179.18	179.893	0.25205	0.25205	180	179.244	180.756	false
77	—	1	179	179.625	0.25205	0.25205	180	179.244	180.756	false
78	—	1	180.16	179.786	0.25205	0.25205	180	179.244	180.756	false
79	—	1	179.76	179.778	0.25205	0.25205	180	179.244	180.756	false
80	—	1	180.35	179.95	0.25205	0.25205	180	179.244	180.756	false
81	—	1	181.03	180.274	0.25205	0.25205	180	179.244	180.756	false
82	—	1	180.32	180.288	0.25205	0.25205	180	179.244	180.756	false
83	—	1	181.19	180.558	0.25205	0.25205	180	179.244	180.756	false
84	—	1	179.89	180.358	0.25205	0.25205	180	179.244	180.756	false
85	—	1	181.41	180.673	0.25205	0.25205	180	179.244	180.756	false
86	—	1	180.66	180.669	0.25205	0.25205	180	179.244	180.756	false
87	—	1	180.11	180.502	0.25205	0.25205	180	179.244	180.756	false
88	—	1	180.23	180.42	0.25205	0.25205	180	179.244	180.756	false
89	—	1	180.13	180.333	0.25205	0.25205	180	179.244	180.756	false
90	—	1	179.83	180.182	0.25205	0.25205	180	179.244	180.756	false
91	—	1	179.64	180.02	0.25205	0.25205	180	179.244	180.756	false
92	—	1	181.1	180.344	0.25205	0.25205	180	179.244	180.756	false
93	—	1	180.7	180.451	0.25205	0.25205	180	179.244	180.756	false
94	—	1	180.41	180.438	0.25205	0.25205	180	179.244	180.756	false
95	—	1	179.75	180.232	0.25205	0.25205	180	179.244	180.756	false
96	—	1	180.92	180.438	0.25205	0.25205	180	179.244	180.756	false
97	—	1	180.09	180.334	0.25205	0.25205	180	179.244	180.756	false
98	—	1	180.97	180.525	0.25205	0.25205	180	179.244	180.756	false
99	—	1	180.49	180.514	0.25205	0.25205	180	179.244	180.756	false
100	—	1	180.29	180.447	0.25205	0.25205	180	179.244	180.756	false
101	—	1	180.52	180.469	0.25205	0.25205	180	179.244	180.756	false
102	—	1	179.95	180.313	0.25205	0.25205	180	179.244	180.756	false
103	—	1	180	180.219	0.25205	0.25205	180	179.244	180.756	false
104	—	1	180.78	180.387	0.25205	0.25205	180	179.244	180.756	false
105	—	1	180.09	180.298	0.25205	0.25205	180	179.244	180.756	false
106	—	1	180.06	180.227	0.25205	0.25205	180	179.244	180.756	false
107	—	1	180.65	180.354	0.25205	0.25205	180	179.244	180.756	false
108	—	1	180.9	180.518	0.25205	0.25205	180	179.244	180.756	false
109	—	1	181.23	180.731	0.25205	0.25205	180	179.244	180.756	false
110	—	1	179.92	180.488	0.25205	0.25205	180	179.244	180.756	false
111	—	1	179.88	180.306	0.25205	0.25205	180	179.244	180.756	false
112	—	1	180.31	180.307	0.25205	0.25205	180	179.244	180.756	false
113	—	1	181.98	180.809	0.25205	0.25205	180	179.244	180.756	true
114	—	1	180.83	180.815	0.25205	0.25205	180	179.244	180.756	true
115	—	1	180.72	180.787	0.25205	0.25205	180	179.244	180.756	true
116	—	1	180.55	180.716	0.25205	0.25205	180	179.244	180.756	false
117	—	1	181.28	180.885	0.25205	0.25205	180	179.244	180.756	true
118	—	1	180.84	180.871	0.25205	0.25205	180	179.244	180.756	true
119	—	1	181.62	181.096	0.25205	0.25205	180	179.244	180.756	true
120	—	1	181.88	181.331	0.25205	0.25205	180	179.244	180.756	true

Control chart signal details

The listed observations 113–115 and 117–120 exceed the EWMA upper limit. These related late signals indicate a sustained rise relative to the historical reference. Link the observation numbers to collection times before investigating the sealing jaw.

Control chart signal details · 7 rows
Observation / subgroup	Chart	Rule
113	EWMA	Beyond limits
114	EWMA	Beyond limits
115	EWMA	Beyond limits
117	EWMA	Beyond limits
118	EWMA	Beyond limits
119	EWMA	Beyond limits
120	EWMA	Beyond limits

Signal observations are displayed starting at 1.

7. Create a report

Keep the EWMA chart, EWMA summary, EWMA values and control limits, and Control chart signal details. Record the source of the 180 °C mean and 0.60 °C standard deviation and what you checked around observations 113–120.

Choose Add to report from the completed run. Open Choose individual items and advanced options to select tables and charts, then choose Add to draft. Hidden items stay in the saved analysis.

Name the report and add the purpose of the study and your interpretation. Choose Save, review Preview, then use Export → Download HTML. The example below contains the full selected content, including results beyond one screen.

Complete native output for this Help example, including applicable tables, charts and run notes. Report numbers use the app’s displayed precision. Exported charts are static. On narrow screens, scroll wide charts and tables sideways.

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