--- title: Choosing a product — ranking and sizing description: How competing families are ranked, how a size is chosen, and how a ruled-out family is followed by its alternatives. sidebar: label: Choosing — ranking and sizing order: 8 --- 4 rules, in register order, from R27 to R88; numbers do not run in sequence. [Back to the index](/business/business-rules). ## R27 — Families that do the same job compete, narrowed to the name or the category first Flow meters and rotameters both measure flow; level indicators, transmitters and switches all measure level. On a line that names no family, only the narrowed pool is listed (the families the generic name points to, else the line's category) while anything in it fits. When none of a generic name's families fits, the line is a deviation (R26). So is a line whose enquiry names different families in different places, two of the same category included, when none of the families it points to fits. The least ruled-out of them leads, with the notice that the name conflicts. When none of the line's category fits, the list is widened to the whole job, with a notice saying so. Accessories are a category with no job: their families are never ranked against each other. A family the enquiry names is listed as named. A line that asks only for an accessory, such as a mating flange, a manometer or an IoT device, is quoted as its own line, and a person picks its family and item code from the Accessories category; once picked, that family is the only one listed, is sized at its item code, and the line is confirmed like any other. An accessory named as part of a meter line stays with that meter. A family must give the output the line asks for (indicate, transmit or switch), read from the line's category, its instrument tag (FT transmits, LG indicates, LSH switches) or its stated output. A line that asks for one readout, analogue or digital, leaves out a family marked with the other (R124); a family marked both, or not marked, is never left out. An indicating transmitter (LIT, PIT) asks for a transmitter, not for indicate and transmit; a category with no outputs set gates nothing; a tag-plate material written as "Tag: SS304" asks for nothing. A transmit or switch tag (for example LT-101) drops the category's default ask for a local readout, because the tag names the instrument's function. A line that states a C-C distance or insertion length leaves out a family whose datasheet has no such entry; a family with no datasheet entries is never left out this way. A stated float size the datasheet does not offer only warns. Families offered only when named, such as the open-channel flowmeter, the orifice plate, the portable, clamp-on and insertion ultrasonic flowmeters, and the bypass glass and metal tube rotameters, are not listed unless the line names them. A companion-only family, such as ORF flange assembly, is never listed, even when named; it follows its parent. A line that asks for an orifice flange assembly, orifice flanges, an orifice plate assembly or an orifice set names the orifice plate, quoted with its flange assembly. A family is offered only while it and its datasheet are in use. This holds in the list of families for a line, the family a reviewer picks, the item code a reviewer jumps to, and a line added by hand, even when the line names the family. A line that already holds such a family as its pick keeps it, marked as no longer in use. A family with no datasheet is not affected. Whether a family is offered only on demand, and the words that ask for it, are set on the family's page; its own name always counts. The on-demand choice applies at once, on every line without a reviewer's pick; changes to the words, and to whether each counts anywhere, apply to enquiries read afterwards. A general name that covers several families, such as "pressure transmitter" for the smart and the miniature pressure transmitter, counts as naming a family offered only when named only if every family it covers is offered that way, as "bypass rotameter" does, including beside other names on the same line. Such a family can also be marked offered on steam: it is then listed on a line whose fluid is steam; a line whose phase is not known is not steam, nor is a line whose fluid is condensate. A word marked to count anywhere asks for its family on every line of that family's category when it appears anywhere in the email the lines were read from (its subject, body and attachments), unless the client negates it there; asking does not name the family. A line, its document and the enquiry's subject or body read the word the same way when they name a family: "Non-IBR", "IBR: No" or "IBR not required" names nothing there, so "Non-IBR vortex flowmeter" stays the vortex flowmeter. A label such as "IBR required:" counts only when its answer says yes, and within the subject, the email body with the requirements read from it, or the attachments with theirs, an answered label outweighs a passing mention; a conditional "as applicable" or "if required" does not count. The IBR vortex flowmeter is offered only when the email asks for it, by IBR, boiler, Indian Boiler Regulation or Indian Boiler Regulations, and only on a steam line that is not condensate. A steam line in such an email leads with the IBR vortex flowmeter and keeps the vortex flowmeter listed below it as an alternative; a water line or any other line that is not steam keeps the meters it would have had, and the email's IBR or boiler ask does not bring the IBR vortex flowmeter in there, so "boiler feed water" keeps its electromagnetic flowmeter. A line whose own text names the IBR vortex flowmeter is the client's explicit choice and keeps it, whatever its phase. Where the IBR vortex flowmeter's datasheet is inactive, the vortex flowmeter stays. A steam line in an email that does not ask for IBR is suggested the vortex flowmeter, which is Non-IBR Certified. An explicit "Non-IBR" or "IBR: No" anywhere in the email cancels the boiler words: the vortex flowmeter is suggested and the IBR vortex flowmeter is not. The cancellation runs one way: a negated boiler ("boiler not in our scope") cancels only the boiler word, never an explicit IBR ask such as "IBR approved". A steam line whose phase is not known is not a steam line here, so it stays on the standard vortex flowmeter. The miniature pressure transmitter only when asked for by name or by one of its words, such as mini, miniature or pencil; the differential pressure transmitter only when asked for by name or by one of its words, such as DPT, differential pressure transmitter or dp transmitter. A steam line that names the vortex flowmeter in an email that asks for IBR is the IBR vortex flowmeter's: the IBR words stand in for the vortex flowmeter, and a line reading "IBR vortex" names the IBR vortex flowmeter alone. A name in the line's document, or in the enquiry's subject or body, asks as well. A line saying "pressure transmitter" alone is the smart pressure transmitter's, never the miniature's. The bypass rotameters have one other way in: they become eligible when no glass tube rotameter reaches the line's flow because the flow is above every tube's range, since a bypass rotameter is made to the client's flow (R88). Eligible, they rank with the rest, and a narrowed pool or another category's pool that still fits can hide them. A family can need inputs of its own: the top mounted level switch is listed only on a line that states its stem length or the height of a switching point, since its stem is cut to them. A line that names it keeps it as the pick and is asked for the stem length; a general name such as "float type" does not count as naming it. A side mounted switch takes one set point: a line stating more rules it out (R23). ## R28 — Among families that fit, the order is: meeting the accuracy the enquiry asks for, orderable from the line's own data, fewer warnings, a family the line calls for (one offered on steam, on a steam line, or one the enquiry asks for), a line that matches one of the family's ideal uses, the smaller error at the line's flow, the lower price, more checked, more sizing headroom, the widest margin to its nearest limit, then catalogue order A family that misses the accuracy the enquiry asks for (R123) ranks behind every family that meets it, ahead of the rest of this order. When the pick leads on that, the reason shown says the family meets the accuracy the enquiry asks for, and the one below it misses it; when the pick leads on the smaller error, it says it is more accurate. A family's error is read from its **Accuracy** specification in Product Limitations, which holds the figure Flowtech's guide states: a percentage of the measured value, of the rate or of the reading is the error itself, a range such as 0.5–1.67% counting as its upper end; a percentage of full scale (FSD) is taken at the line's operating flow, on the full scale of the size chosen for the line. An accuracy in millimetres, "visual indication only", or none is not known. Its price is the base price of the item code it is sized to, or of the price band holding the line's highest flow in the water equivalent the size was chosen on, without option rates. Errors are compared to a hundredth of a percentage point, so 1% and 1.004% are level. A family whose error or price is known ranks ahead of one whose is not; two not known are level and the next measure decides. An error is not known for an accuracy of full scale when the line states no single or operating flow, or when the family is not sized from the line's flow; a price is not known when the family is sized to no released item code, the code has no price, or no price band holds that flow. On level switches, a displacer is ideal for two set points and a top mounted switch for three or more. Warnings still rank first, and a general name such as "float type" keeps its own pool (R27). A family can have several ideal uses; the line matches it when it fits any one of them, every entry of that use for the line's phase passing. An entry that fails, or that cannot be checked for want of a value, leaves that use unmatched. A family is orderable when a released code at a size worked out from the line's own values, or an option chosen from them, can be quoted as it stands. A named family that fits a line missing a key input reads as unverified, never as confirmed; every line lists the key inputs it lacks. Each instrument type names its own key inputs, from fluid, flow, line or connection size, temperature, pressure and a level's span: a level switch needs no span, a level indicator needs its connection size, a pressure transmitter needs no size. A temperature or pressure assumed ambient under R17 is not lacking (R16), except the pressure of a pressure instrument, and nor is a fluid the line names but the library does not hold, once the line states its density or specific gravity. Nor is the flow, when the line's pick is sized at its stated size (R29); the line is not asked for it. A guessed fluid still lacks confirmation. The margin to a limit, and the other measures, are read without an assumed range end or design value (R24). ## R123 — A flow meter or rotameter that cannot meet the accuracy the enquiry asks for warns The accuracy an enquiry asks for is read into the line's Accuracy field, and only from what it states (R122). On a line of the Flow Meters or Rotameters category, each family's error at the line's flow (R28) is compared with it, a figure that names no basis, such as "±1%", read as a percentage of the reading. A family whose error is larger carries a warning naming both and ranks behind every family that meets the figure, ahead of the R28 order. A family the enquiry names that misses it is offered as a deviation, with families that meet it as the alternatives. A line whose pick misses it does not confirm itself (R71); a person can still confirm it. A family whose accuracy is not known, an accuracy in millimetres or in words, and a line of any other category, such as a level or pressure transmitter, are not compared: the stated figure is kept on the line and changes nothing. ## R29 — The size follows the stated line size when it reads the flow, else it is the smallest that reads the whole flow; with no usable flow a flow meter takes the stated size; a flow no size reaches can rule the family out ### Sizing on the line size and the flow When the line states a main line size, or with none a process connection size, a family sized from its flow table takes that size, or the closest size it has an item code for, the larger on a tie, as long as that size reads the flow, or reads the stated figures with the assumed-minimum warning below. Only when it cannot is the family sized on the smallest size that reads the flow. A rotameter line that states no flow but the scale it wants, its Flowtech Flow Range, is sized on that scale's maximum. When the line holds no usable flow (no flow figure, figures written with no unit, or a flow in a unit FlowOS cannot read for its phase), a flow meter sized from its flow table is sized at that stated size instead, on a liquid line whose phase is known and a size within the family's table: the closest size it has an item code for, as above, with the range that size measures and the note "sized on the stated 100 NB; flow not checked". Nothing is checked against the flow, so nothing is ruled out on it. A family priced by its flow range (the glass tube, metal tube and acrylic body rotameters) still needs a flow, since the flow chooses its tube and price band, and so do gas and steam lines, whose range depends on the operating point. The flow runs from the highest figure the line states down to a stated minimum. With no minimum stated, or a minimum of zero, which no meter reads, the minimum is taken as 0.7 × the normal flow, the lowest operating figure below the maximum; with no normal flow, as 0.6 × the maximum. A lower figure the line states sets the minimum instead. Either minimum is assumed: when no size reads down to it but one reads the stated figures, the family is sized there, stays orderable and warns that the assumed minimum lies below the size's range. A velocity or Reynolds limit breached only at the assumed minimum warns and rules nothing out; a stated normal flow between that minimum and the maximum is judged too, and a breach there rules the family out. A meter smaller than that stated size warns that reducers are needed, and a stated size whose own meter cannot read the flow warns that the line looks mis-sized. A tube meter's connection is matched at the process connection size when the line states one, else at the main line size; sizes that follow the line (the double-window and full-view side glasses, orifice plates, the bypass rotameters, and the magnetic and tubular level indicators) use the main line size, else the process connection size. A stated size with no item code is quoted on the next size up, with a note saying so; with no bigger size it is not orderable. ### Size fields, options and single item codes A family sized by one of its options, such as a pressure transmitter's pressure range or a clamp-on flowmeter's sensor size, takes the released item code made for that option, else the family's only code, which covers its whole range with the option in its model number; an option neither gives is still chosen, says it has no released item code, and leaves the line without a size to confirm with (R75). A family with a single item code is always orderable with it: its size field is an option the line sets, and it reads "sizing not available" or "can't size yet" only when it has no code or more than one; a stated value no option covers still rules it out. A size field written in inches, such as 1-1/2", 1½″ or 2 in, is read as its nominal bore on the pipe table (40 NB, 50 NB); a bare fraction, or wording naming two sizes, gives none. A line with no size field takes the one NB, DN or inch size its own text names, as in "Glass Tube Rotameters 80NB" or "LINE SIZE: 8\"", as the main line size; text naming two different sizes gives none, and a length in mm is not a size. The side mounted level switch takes its float from its process connection size: the 36 × 100 float for a 40 NB flange and the 48 × 100 float for 50 to 80 NB; no float covers another size, which rules the switch out. The top mounted level switch takes its float and float pipe the same way: the 25 × 25 float and 10 mm pipe for 25 to 40 NB, the 48 × 48 float and 14 mm pipe for 50 to 80 NB. A vortex flowmeter on a liquid that would cavitate at its size is sized up while a larger size still reads the flow (R100). ### When sizing rules a family out Sizing rules a family out when no size reaches the flow worked out from stated, saved or library values, the assumed minimum left out. It only warns when that flow rests on an assumed flow, pressure, temperature, density, phase or table basis (the turbine, acrylic-body and metal-tube rotameter families), or when a table could not be read. It also rules a family out when no listed range covers the stated values and every option has a range (a family that also offers a custom range is only warned of). A family whose only table is for another phase than the line's, a liquid table for a gas or steam line, is left unsized, never ruled out. A float the fluid grades C or D is sized on with a warning naming the grade, after the floats it grades better; whether the grade rules the family out is R30's alone. A rotameter cannot be sized for steam; sizing leaves it on the list, unsized. ### Steam lines A steam line is sized on its density, which comes from the first of these the line holds: a stated density; steam properties (IAPWS-IF97) at the operating pressure and temperature, when both are held and the temperature is above saturation; saturated steam at the pressure alone; a stated temperature at or below saturation at that pressure, taken as saturated, with a warning; saturated steam at the temperature alone. An assumed value, such as an assumed ambient temperature or pressure, does not count as held. A steam line holding none of pressure, temperature or density can't be sized: "steam needs its operating pressure, temperature or density". Above 100 bar abs it can't be sized either. The client's steam reference, printed in kg/h for fourteen pressures, is used as printed: the column nearest the line's density is read, its figures scaled by the line's density over the column's, and a line at a printed saturated pressure reads its column as printed. A line whose density lies outside the columns' (for saturated steam, a pressure outside 2 to 20 bar abs) is read on the nearest column, scaled. Its size and its Flowtech flow range are assumed, and a range no size covers there warns instead of ruling the family out. ### Flow tables Where a family's flow tables differ by a datasheet option, such as the wetted material, the table is the one for the option the line states; else the one for the option the family's datasheet settles on; else the other tables, with the caution "sized on the ... table: the ... table can't read the flow". When sizing falls back to another option's table, that option is set in the datasheet with the reason "sized on the ... table" and is still graded against the fluid, so the datasheet and the size agree. A stated option with no table is sized on the others, with the caution "no table for the stated ...". ## R88 — A named family that is ruled out is followed first by its try-next families, in their order This holds whatever rules the family out: a limit, its line sizes, a gate, or no size that reads the flow on a table not marked assumed. The rules still apply to each of them: a bypass rotameter named on a line below 50 NB is followed by the metal tube rotameter. The bypass rotameters are the exception to being listed only when named. Naming the bypass glass tube lets in that family only, and naming the bypass metal tube that one only; a general name such as "bypass rotameter" names both. Otherwise they become eligible only when the line's flow is above every glass tube's range: a glass tube rotameter named for such a flow is cautioned, not ruled out (its sizing basis is marked assumed), and stays the pick, with the bypass glass and bypass metal tubes listed beside it and ranked as R28 says. A glass tube ruled out while it reads the flow brings neither, and neither does a glass tube one of whose tables could not be read, a stated span wider than any one tube covers, or a flow below the smallest tube. A reviewer's pick of a glass tube for a flow above every tube brings them as well. A try-next family that leads this way is shown as listed first as the substitute for the family asked for, also over another try-next family that ranks higher, since the list's order decides. After them come the other families, ranked as R28 says. The lists are kept on the Product Limitations screen. The glass tube rotameter's is the bypass glass, then the bypass metal tube rotameter; their own flow ranges are not held yet, so, when the glass tube is ruled out and they lead the list as families, each says "no flow range held yet". Each bypass rotameter lists the metal tube rotameter. The electromagnetic flowmeter's is the vortex, then the turbine flowmeter.