Standard decision rule and measurement uncertainty
FAKT as a standard decision rule apply the “Simple Acceptance Criteria” together with indirect accounting of measurement uncertainty. Simple acceptance is also called “shared risk” because the probability to be outside the tolerance limit may be as high as 50% in the case when a measurement result is exactly on the tolerance limit (assuming a symmetric normal distribution of the measurements). Under such rule, the test laboratory and customer of the measurement result agree, implicitly or explicitly, to accept as conforming (and reject otherwise) a test result whose property has a measured value in the tolerance interval.
In order to keep the chances of incorrect decisions to levels acceptable, an upper limit for measurement uncertainty Umax in accredited test procedures is deemed to be agreed with the customer.
These values are actually as follows:
Applicable for temperature exposure tests:
| Measurement condition temperature T: | Umax(T)≤2°C |
| Measurement condition time t (for values up to 100 s): | Umax(t)≤1s |
| Measurement condition time t (for values above to 100 s): | Umax(t)≤10s |
Applicable for temperature exposure tests with humidity:
| Measurement condition temperature T: | Umax(T)≤2°C |
| Measurement condition relative humidity RH: | Umax(RH)≤5%RH |
| Measurement condition time t (for values up to 100 s): | Umax(t)≤1s |
| Measurement condition time t (for values above to 100 s): | Umax(t)≤10s |
Applicable for corrosion tests (salt spray tests):
| Measurement condition temperature T: | Umax(T)≤2°C |
| Measurement condition pH-value: | Umax(pH)≤0,07 |
| Measurement of volume V: | Umax(V)≤1ml |
| Measurement condition time t (for values up to 100 s): | Umax(t)≤1s |
| Measurement condition time t (for values above to 100 s): | Umax(t)≤10s |
Applicable for IP-protection tests water ingress:
| Measurement condition temperature T: | Umax(T)≤2°C |
| Measurement condition flow rate Q: | Umax(Q)≤5% |
| Measurement condition pressure p: | Umax(p)≤5% |
| Measurement of length l: | Umax(l)≤10mm |
| Measurement condition time t (for values up to 100 s): | Umax(t)≤1s |
| Measurement condition time t (for values above to 100 s): | Umax(t)≤10s |
Applicable for IP-protection tests foreign objects (dust ingress):
| Measurement condition temperature T: | Umax(T)≤2°C |
| Measurement condition flow rate Q: | Umax(Q)≤5% |
| Measurement condition pressure p: | Umax(p)≤1mbar |
| Measurement condition time t (for values up to 100 s): | Umax(t)≤1s |
| Measurement condition time t (for values above to 100 s): | Umax(t)≤10s |
Applicable for IP-protection tests against foreign access (probes) and against access to hazardous parts:
| Measurement condition force F: | Umax(F)≤10% |
The expanded uncertainty U is indicated for a coverage factor k=2.