Low-cost string pot sensor

General purpose cable extension sensor  has flexible built-in options in a compact durable housing

Variohm EuroSensor's new SP3 String Pot sensor from Celesco Inc. features a rugged cable extension design with a plastic-hybrid precision potentiometer and winding drum in an economical and flexible package that can be user configured for a choice of 4-20 mA or 0-10 VDC output by simply connecting the appropriate signal wires on installation.

With precision absolute linear position measurement in a choice of four ranges covering 120 mm, 315 mm, 635 mm and 1270 mm, the extremely compact unit can be mounted within an envelope of just 25 mm wide x 50 mm deep x 90 mm high and its durable water resistant polycarbonate housing has four point fixing and an optional (or is it included?) bracket that facilitates universal mounting. The cable extension sensor  requires no critical cable alignment which suits difficult to measure applications where there is no space to fit more traditional measurement devices or where the moving components may be submerged or obscured by other equipment.

The SP3 has an acceleration rating of up to 15g in retraction and a rated life of over 2.5 million cycles for the 120 mm travel unit (250K cycles for the 1270 mm travel version).  Overall accuracy is between 0.25% to 1.0% FS depending upon stroke length, repeatability better than 0.05% FS, and the measuring resolution is essentially infinite.  

The supply voltage is 8 – 40 VDC for the current output version and 12 – 32 VDC for the voltage version. Electrical connection is via a 1 metre multi conductor cable.

With competitive pricing and stock availability from Variohm, the SP3 offers high reliability and ample levels of precision for many applications in light industrial machinery and OEM equipment.

Gearshift indication in racing

West Surrey Racing choose Variohm cable-extension transducers for neat gearshift indicator solution
When West Surrey Racing (WSR) needed a rapid solution to improve the gearshift indicator system on its FIA World Touring Car Championship BMW 320si, they chose MTA series cable-extension transducers from motorsports sensor specialists Variohm EuroSensor. The neat solution was delivered on the same day as the initial enquiry, in time to meet the deadline for FIA race approval, and easily installed and electrically interfaced to a simple dashboard display to indicate the selected gear from the gear stick position.

The compact miniature 'stringpot sensor' from Celesco was chosen for its installation simplicity and robustness. The 35 mm diameter x 13 mm thick sensor provided the distance measurement directly from the BMW's H-pattern 5-speed gearshift mechanism without the need to ensure precision alignment, with the integral spring loaded stainless steel cable simply connected to the gear stick. The IP55 rated aluminium housed unit was supplied on an optional mounting bracket that was fixed in a slightly offset position on the car chassis to ensure each gear position returned a different position reading.

WSR chose the smaller of two MTA models with a 75 mm stroke and voltage divider (potentiometer) output powered from the car's 12 VDC supply. The high duty cycle conductive plastic potentiometer has an essentially infinite resolution and very long working life, and with a full stroke accuracy of better than ±0.4% and repeatability of ±0.02%, it provided more than adequate performance for the application.

With demanding applications in areas such as heavy construction equipment and agricultural machinery, the MTA series is well suited to the arduous environmental conditions that the BMW typically sees throughout a race.

WSR is based in Sunbury-on-Thames (GB) and in addition to its eBay-backed FIA WTCC BMW 320si race team, also competes in the British Touring Car Championship and provides R&D, CAD and engineering services throughout the motorsports industry that can accommodate anything from one-off performance prototypes to 'Limited Edition' production.

Variohm EuroSensor also supplies WSR with ride height position measurement solutions using its race proven ELPM series linear slimline linear position transducers. The compact rod-type ELPM provides stroke lengths up to 75 mm in IP67 sealed housings.

Cable extension position

New low-cost cable extension position sensor series now available with incremental encoder

Celesco's SR1 series low-cost/high performance string pot sensors are now available with an incremental encoder measurement source. The SR1E, available exclusively from sensor specialists Variohm EuroSensor, has a measuring range up to 3 metres with a resolution of 100 pulses per 25 mm of travel (+/- 2 pulses). With IP67 protection rating its tough polycarbonate enclosure is built for outdoor and wet environment applications in construction equipment and industrial position sensing, and includes built-in mounting flexibility where the user can freely select mounting position, cable exit and connector orientation on installation.

The Celesco SR1 range now includes encoder, voltage divider and user programmable 4..20 mA and VDC versions with electrical and mechanical flexibility that allows users to select a single low-cost product solution across many general purpose applications for cable extension based position sensing. The 'one-size-fits-all' SR1 range can eliminate the customers’ need to specify and purchase multiple stroke ranges and offer benefits of simplified stock and lower unit cost.

Specific to the new SR1E encoder version, a 5...30 VDC push-pull driver covers a wide choice of supply voltages and electrical connection is via an M12 – 4-pin connector with mating plug supplied and 4 m cable sets are available on request.

The maximum velocity for the sensor is 2 m/sec with maximum acceleration at 10 g with an operating temperature from -20ºC to +85ºC. The overall accuracy for SR1E is +/- 0.1% F.S. and repeatability to +/- 0.05% F.S. Custom encoder resolutions are also available on request.

As with all string pot or cable extension sensors from Celesco, installation is very straightforward with no critical alignment required. The nylon coated stainless steel cable is fully spring loaded, is easily attached to the object under motion and fully retracts into the body of the SR1E ensuring a compact installation envelope of around 200 x 120 x 100 mm (w x h x d).

Miniature cable extension position sensor for wet and severe environments

Variohm EuroSensor has added a new cable extension linear position sensor from its distribution partner, the USA 'string pot' sensor specialist Celesco Inc. The MT3A is particularly suited to precision distance measurement up to 750 mm in potentially wet and severe application environments. The rugged sensor features an O-ring sealed and IP67 rated anodised aluminium enclosure with a polycarbonate cover and a nylon-coated stainless steel measurement cable. With a choice of three cable tension options to suit linear position measurement in acceleration conditions of 17g, 50g or 90g, it is well matched for demanding automotive/autosports and aerospace test applications such as crash testing, structural component evaluation and off-road suspension testing .

Furthermore, an extended temperature range of -40 to +125 ºC allows use in all-weather outdoor environments and as the MT3A can withstand temporary immersion in water and washdown situations, its use across harsh industrial applications is also possible. For extreme high impact applications, an optional anodised aluminium cover is available.

The conductive plastic-hybrid potentiometer sensor provides a voltage divider output from an input voltage up to 30 VDC, with effectively infinite positioning resolution and full stroke accuracy up to +/- 0.25% , and repeatability to +/- 0.02%.

For mounting flexibility the MT3A features an integral 2-axis, 360° freely rotating mounting bracket, and measuring within a volume of under 62 mm x 41 mm x 45 mm (LxDxH), it is easily installed in space restricted areas.

The sensor is available in four measurement ranges of 0 .. 75 mm, 0 .. 225 mm, 0 .. 375 mm and 0 .. 750 mm. Electrical connection is via strain relief cable (4.5 m or 9 m length) in a choice of end, top or side mounting. Customers can also specify a plain cover option to provide their own cabling arrangements.

Long travel range cable-extension position sensors

Celesco's PT9000 cable extension position sensors are packed with application flexibility for real heavy-duty, high-accuracy linear measurement up to 43 metres.

Used on indoor, outdoor and wet environment applications as diverse as material handling, water & waste treatment, hydraulic cylinder positioning and crane control, the modular PT9000 series 'String Pot' sensor includes possibly the widest selection of features available on any standard cable extension position transducer today. The extensive choice of models and options covers IP67 or IP68 sealed aluminium or stainless steel housings, several industry-standard output signal options and a comprehensive selection of electrical interfacing.

The standard version has eleven measurement range options from 0 to 14 metres with an optional extended range to around 43 metres. The operating temperature spans -40°C to +90°C, and the vibration rating is 10G at 2000 Hz. Guaranteed best position accuracy is 0.1% of full stroke with repeatability to 0.02% of full stroke.

Throughout the range, the drum mounted durable plastic-hybrid precision potentiometer, with a 250,000 minimum rated cycle life, is factory configured for a choice of electrical output covering voltage divider, position/velocity output (with additional tachometer), 0/4...20 mA, and 0...10 VDC. An incremental encoder version is also available with positioning resolution from 10 to 250 pulses per inch of travel. Furthermore, CanBus and DeviceNet compatible output versions may also be supplied.

Additional options include a redundant brush system that offers extra protection for extraordinarily dirty environments and a velocity limiting system that prevents the cable from reaching damaging velocity during a free-release. Up to seven electrical connection options are available for each output version – from plastic or metal connectors to fully pressure tested waterproof cable.

To match application requirements the PT9000 series is also available in a choice of powder-painted aluminium or 303 stainless steel housings with IP67 or pressure tested IP68 rated protection from immersion in liquids. Hazardous area certification is also available and measuring cable options further nylon-coated stainless steel, stainless steel only or thermoplastic cable.

The Celesco PT9000 series typically requires just 150 mm width to install with a generous tolerance of misalignment between the cable fixing point and the housing. The design also caters for a choice of four with four cable exit options.

These are available exclusively in Britain from Variohm EuroSensor,