The Foxboro IDP10M and IDP05S measure the same differential pressure with the same sensing philosophy — and exist for the reason all instrumentation families tier themselves: consequence. The IDP10M carries the premium class (±0.075%-class accuracy, 400:1 turndown) for loops where error is money; the IDP05S delivers the value tier with ATEX certification for the honest majority of monitoring points. Choosing between them is a grading exercise, and grading honestly is where the savings live.
What the premium tier buys
Accuracy held at the working point across the turndown the loop actually runs — the reference class the datasheet states. On balance points, custody boundaries and control loops whose error propagates into product — the IDP10M's class is the spec. The premium also buys the documentation depth those loops' audits expect: calibration behavior, stability statements, the paperwork that makes the number defensible.
What the value tier buys
The same architectural honesty at monitoring class: ±0.075%-class accuracy in its span, ATEX builds for the hazardous locations that populate real plants, and a price that lets the plant instrument every point instead of every third point. The IDP05S is not a compromise; it is the tier most points deserve.
The decision rule
Grade each DP point by what its error costs: money flows and control-critical loops — IDP10M; monitoring, alarming, indication — IDP05S. Plants that grade honestly run both tiers as a portfolio, and the measurement layer stays consistent because the families share their engineering DNA.
Is the value tier accurate enough for pump protection?
Protection trips on thresholds, not on fractions of a percent — the IDP05S class covers suction and discharge monitoring comfortably. Reserve the premium tier for the loops whose numbers get argued about.
Does ATEX cost accuracy?
The certification constrains the electronics design, not the metrology — the IDP05S's accuracy class is its own statement. The real ATEX cost is approval scope and lead time, which is why grading the location's zone honestly matters as much as grading the loop.
