Turbine flowmeter pickoff (pickup coil): magnetic reluctance, modulated-carrier RF and amplified heads
The pickoff that turns turbine-rotor blade passes into a signal · variable-reluctance coil, modulated-carrier (RF) head, or a pickoff with its own amplifier
A turbine flowmeter body carries a bladed rotor; what turns its rotation into a usable signal is the pickoff (pickup coil) threaded into the body above the rotor. There are two sensing principles: a variable-reluctance coil, in which a permanent magnet and winding generate a small AC voltage as each blade passes, and a modulated-carrier (RF) coil, in which the blades modulate a high-frequency carrier from an external oscillator. Either can be bought as a bare coil feeding a separate amplifier, or with the amplifier built into the head. The choice sets the low-flow range, the signal level on the cable and the temperature the head can take.
Pickoffs (pickup coils) and amplified pickoff heads that mount in turbine flowmeter bodies and convert rotor blade passes into a frequency signal, with the carrier and pulse amplifiers that condition them. Complete flow meters of all measuring principles are covered on the Flow meter page, and low-range sensors for fertilizer concentrate lines on the Flow sensor for liquid fertilizer injection page. Turbine meter bodies, rotors, totalisers and flow computers are outside this page.
CNFX editorial research · Sources checked October 12, 2026 · 4 sources
Variable-reluctance coil: 1.5 kΩ winding, 900 gauss magnet, 30 mV to 3 V AC with no power supply
Blancett's B111109 is a variable-reluctance magnetic pickoff with a 5/8"-18 thread, built to replace 3030AN-type pickoffs on its Model 1100 turbine meter and for heavy-duty industrial use. It needs no power supply and generates a 30 mV to 3 V AC sine wave; its DC coil resistance is 1.5 kΩ ±10% (700 mH maximum) and its magnetisation 900 gauss ±20%. [1]
The shell and bottom are 303/304 stainless steel with solid internal potting, the connector is a 2-pin gold-plated type mating with MS 3106-10SL-4S, and the T-3 temperature rating is −150 to +325 °F, or 350 °F on a 1000-hour intermittent duty rating. [1] Editorial calculation: −150 °F ≈ −101 °C and +325 °F ≈ +163 °C.
A sine wave this small is squared into pulses before it is sent down a long cable. Flow Technology's PA04 pulse amplifier for magnetic pickoffs lists an input sensitivity of 4 to 10 mV p-p, a differential input impedance above 5 kΩ and a 0 to 10 V pulse output, and the company states that conditioned signals can travel more than 1000 ft depending on the environment. [2] Flow Technology names magnetic drag as what limits small meters at low flow (next section), and Hoffer gives a 10:1 to 25:1 flow turndown for its meters fitted with a magnetic coil, depending on meter size and bearing type. [4]
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Modulated-carrier (RF) pickoff: a carrier near 45 kHz, no magnetic drag, turndown up to 100:1 on ball-bearing meters
In the modulated-carrier arrangement the amplifier generates the carrier and the passing turbine blades modulate it, which Flow Technology says removes the effect of magnetic drag and extends the range and linearity of small meters at low flow. Its CA04 carrier amplifier runs an oscillator at approximately 45 kHz and accepts blade frequencies of 5 to 3500 Hz. [2]
The CA04 ordering code has a separate input option for other makers' RF pickoffs that have 330 µH coils, and Flow Technology notes that its input figures depend on the transducer and signal level and are not guaranteed for every transducer or meter, so an RF head and a carrier amplifier should be bought as a matched pair. [2] Hoffer states that its turbine meters with a modulated-carrier coil give a usable flow range of up to 100:1 when the meter has ball bearings, against 10:1 to 25:1 with a magnetic coil. [4]
Signal chain
Sensing
Figures stated
Magnetic coil → PA04
Magnet and coil generate a sine wave
Input 4–10 mV p-p, > 5 kΩ; output 0–10 V pulse at 10–32 VDC [2]
RF coil → CA04
Blades modulate an amplifier-generated carrier
Oscillator ≈ 45 kHz; input 5–3500 Hz; output 0–10 V at 19–32 VDC, 0–8 V at 11–22 VDC [2]
Turndown (Hoffer meters)
Magnetic vs RF coil
10:1 to 25:1 vs up to 100:1 with ball bearings [4]
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Pickoffs with the amplifier inside the head: pulse output, supply range and 85, 125 or 140 °C bodies
Putting the conditioner in the pickoff housing removes the meter-top junction box. Hoffer's Redi-Pulse coil, offered in magnetic and modulated-carrier versions, outputs TTL/CMOS (0–5 VDC), a 0–10 VDC square wave or open collector from 8–30 VDC at 10 mA maximum (15–30 VDC for the 0–10 V output), covers approximately 10 to 10,000 Hz and, Hoffer states, can be transmitted up to 5,000 ft. [4]
Flow Technology's Amplifier Link combines pickoff and conditioner in a 303 stainless body with a 0–5 VDC pulse output, magnetic or RF electronics selected at the factory, 8–30 VDC power (13–28 VDC for intrinsically safe versions) and an optional integrated RTD for temperature. [3] Hoffer's bulletin lists −40 to 85 °C and −65 to 150 °C for operating and storage temperature of both versions; the layout of the bulletin's text does not make clear which range is which, so confirm with the maker. [4]
Frequency ranges in the Amplifier Link sheet are printed as 'Mag 5-10 kHz' and 'RF 5-5 kHz'; reading them as 5 Hz to 10 kHz and 5 Hz to 5 kHz is an editorial interpretation, so confirm the limits against the meter's full-scale blade frequency.
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Data for a turbine pickoff enquiry
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Meter: [make and model; size; thread for the pickoff, e.g. 5/8"-18; blade count; full-scale frequency]
Sensing: [magnetic reluctance or modulated carrier; lowest flow to be read]
Output: [raw sine wave or amplified pulse; level; supply voltage; cable length]
Environment: [process and ambient temperature; hazardous-area approval]
Connector: [MS 2-pin or 3-pin; pigtail; NPT conduit]
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Does a magnetic turbine pickoff need power?
No. Blancett's variable-reluctance B111109 needs no power supply and generates a 30 mV to 3 V AC sine wave from a 1.5 kΩ coil and 900 gauss magnet. [1]
Why choose an RF (modulated-carrier) pickoff?
The blades modulate an amplifier-generated carrier, about 45 kHz in Flow Technology's CA04, so there is no magnetic drag on the rotor; Hoffer cites up to 100:1 turndown with ball bearings against 10:1 to 25:1 with a magnetic coil. [2][4]
How weak a signal can a pulse amplifier read?
Flow Technology's PA04 lists an input sensitivity of 4 to 10 mV p-p for magnetic pickoffs, with a differential input impedance above 5 kΩ. [2]
How hot can an amplified pickoff run?
Flow Technology's Amplifier Link comes in −40 to 85 °C, 125 °C and 140 °C grades, with 140 °C offered in RF versions only. [3]
Sources and what still needs a direct check
Sources checked 2026-10-12. Coil ratings come from Blancett's B111109 pickoff sheet; carrier and pulse amplifier figures and the amplified pickoff grades from Flow Technology's CA04/PA04 and Amplifier Link data sheets; turndown and integrated-amplifier figures from Hoffer Flow Controls' Redi-Pulse bulletin. Values apply to the models named.
