{"id":8771,"date":"2026-09-22T06:24:29","date_gmt":"2026-09-22T06:24:29","guid":{"rendered":"https:\/\/www.simplybuyglobal.com\/?p=8771"},"modified":"2026-10-13T00:35:39","modified_gmt":"2026-10-13T00:35:39","slug":"pressure-transmitter-turndown-ratio","status":"publish","type":"post","link":"https:\/\/www.simplybuyglobal.com\/es\/industry-knowledge\/pressure-transmitter-turndown-ratio\/","title":{"rendered":"Pressure Transmitter Turndown Ratio: Rangeability & Selection"},"content":{"rendered":"

Quick answer:<\/h2>\n\n\n\n

A pressure transmitter turndown ratio is how far a transmitter can be re-ranged below its widest span. A quote can carry three different figures, because three denominators exist: the widest span, the span you configured, and the capsule’s minimum span. Read the denominator first, then the turndown at which the accuracy is stated. Simply Buy is a multi-brand distributor and supply-chain integrator, not a manufacturer, so the capsule you choose can be matched against the range you can check before it ships.<\/p>\n\n\n\n

This article is for procurement and engineering buyers outside China who specify pressure instruments by part number: distributors, system integrators, EPC project buyers, and plant maintenance teams. By the end, you can name the denominator behind any range figure, restate an accuracy claim at your own span, and write an RFQ that stops a mis-ranged transmitter from arriving. Assumed knowledge: the 4-20 mA loop, zero and span, and the difference between gauge, absolute and differential pressure.<\/p>\n\n\n\n

What Is a Turndown Ratio on a Pressure Transmitter?<\/h2>\n\n\n\n

The turndown ratio, sometimes called rangedown, is how far you can shrink a transmitter’s measurement span from the widest span the device allows. A 0-1000 psi transmitter with a 20:1 ratio can be set as narrow as 0-50 psi. The number only exists on a device with a continuous, re-scalable output, which is why a 4-20mA pressure sensor carries one and an on\/off switch does not (pressure switch vs pressure sensor<\/a>). The sensing element decides which ratios are possible at all.<\/p>\n\n\n\n

The trap: a figure with no span, no pressure type and no accuracy condition is a sales number, not a specification. Three questions fix that: which span the ratio uses, at what turndown the accuracy is stated, and whether your process span fits the quoted capsule.<\/p>\n\n\n\n

What Do URL, Span and Sensor Capsule Actually Mean?<\/h2>\n\n\n\n

Five terms carry every rangeability argument. The URL, or upper range limit, is the highest pressure the device can measure; the LRL, or lower range limit, is the lowest. The URV, or upper range value, is the calibrated top of your range and the 20 mA point, while the LRV, or lower range value, is the calibrated bottom and the 4 mA point. A sensor capsule, or sensor code, is the physical cell inside the housing, and it fixes both the URL and the smallest span the device accepts.<\/p>\n\n\n\n

One worked ratio: a 1000 mbar URL with a 0-100 mbar range has a 100 mbar span, so the ratio is 10:1. The same cell set to -300 to 0 mbar has a 300 mbar span against the same URL, so the ratio is 3.33:1.<\/p>\n\n\n\n

Why Does One Transmitter Have Three Turndown Figures?<\/h2>\n\n\n\n

Because vendors do not agree on what to divide by, and three sourced forms appear in the documents buyers receive.<\/p>\n\n\n\n

Maximum allowable span divided by minimum allowable span is the capability framing used by the Control.com calibration textbook. It describes the range the instrument offers from widest to narrowest, and it does not change when you re-range.<\/p>\n\n\n\n

URL divided by the calibrated span is the setting framing used by instrumentationtools (Transmitter Turndown Ratio, Set Span and Zero Span): what am I asking this device to do now?<\/p>\n\n\n\n

URL divided by the minimum measurement range is the capsule framing used by Fuji Electric (What is the rangeability and turndown ratio of a pressure transmitter?): at its limit, what will this cell allow?<\/p>\n\n\n\n

Which Denominator Should You Use?<\/h3>\n\n\n\n

Use two of them, for two questions. URL divided by your configured span is what you are asking for, and you compare it against the capsule before ordering. URL divided by the capsule’s minimum span is what the capsule allows, and that number decides whether your span is settable at all.<\/p>\n\n\n\n

Skip the second question and the failure is concrete. A transmitter quoted at 20:1 with a 1000 psi URL has a 50 psi minimum span, so a 40 psi process span cannot be set on it, whatever the configuration software suggests. The fix is a different capsule or model, not a different setting.<\/p>\n\n\n\n

Does a Higher Turndown Ratio Mean Better Accuracy?<\/h2>\n\n\n\n

Usually the opposite. Accuracy worsens as an instrument is turned down from its maximum span, and each vendor in the list below bounds it in a banded accuracy law. Reference accuracy is the base figure covering linearity, hysteresis and repeatability, before thermal and static-pressure terms are added.<\/p>\n\n\n\n

The laws differ by vendor, so the accuracy you get depends on the model:<\/p>\n\n\n\n

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  • ABB, 266DSH, codes F to P: \u00c2\u00b10.06% of span at 1:1 to 10:1, then \u00c2\u00b1(0.006 x TD)% up to 100:1.<\/li>\n\n\n\n
  • Siemens, SITRANS P DS III: about (0.005 x r + 0.05)% for measuring span ratio r from 30 to 100.<\/li>\n\n\n\n
  • Endress+Hauser, Cerabar M: up to \u00c2\u00b10.15% of the set span, with thermal terms such as \u00c2\u00b1(0.1 + 0.15 x TD)% of span.<\/li>\n\n\n\n
  • Rosemount, 3051 total-performance bands, Ranges 2 to 4: \u00c2\u00b1(0.025% URL + 0.125% span) at 1:1 to 30:1, then \u00c2\u00b1(0.035% URL + 0.125% span) to 150:1.<\/li>\n\n\n\n
  • Yokogawa, EJA110E: \u00c2\u00b10.055% of span above a capsule threshold, then \u00c2\u00b1(0.005 + a capsule coefficient x URL\/span)% below it.<\/li>\n<\/ul>\n\n\n\n
    \"ABB<\/figure>\n\n\n\n

    The condition that decides which figure applies, the turndown at which it is stated, sits away from the headline number and is easy to miss. Two of these figures are conditioned on 1:1. Endress+Hauser applies its total error to Turndown 1:1, and Siemens states that accuracy is only achieved at maximum measuring span.<\/p>\n\n\n\n

    A worked example: ABB’s F-to-P law at a ratio of 50 gives \u00c2\u00b10.3%, five times the 0.06% the specification table advertises.<\/p>\n\n\n\n

    Whether you can hold that ratio depends on the output. A fixed-span analog transmitter such as the ifm PA3023 ships with its range set. The ifm PN3594 can be re-scaled in the field.<\/p>\n\n\n\n