Level controller

01

Match the switch technology to the medium

Flowline's liquid level switch range lists ultrasonic switches for chemicals, solvents and light oil, vibration switches for wastewater, capacitance switches for water and conductive chemicals, buoyancy switches for clean water and chemicals, optic leak switches for water and translucent chemicals, and multi-point switches up to 10 ft (3 m) long for day tanks, skids and sumps. They run on 12–36 VDC or 120/240 VAC with SPST or SPDT relay or reed contacts rated 15 VA (0.25 A), 60 VA (1 A) or 250 VAC at 16 A on the high-power models, in NEMA 4X (IP65) or NEMA 6 (IP68) housings of PP, PVDF, PFA or Ryton, rated −40 to 80 °C and atmospheric to 150 psi (10 bar) depending on the model. [1]

VEGA's capacitive VEGAPOINT switches cover water-based liquids, sticky and adhesive media and light bulk solids, with three-wire transistor output, IO-Link listed on the sticky-media, water-based (Ex/ship) and light-bulk-solids versions but not on the basic water-based version, ½ in threads with hygienic adapters, M12 or ISO 4400 connectors, a 360° illuminated status ring, and hygienic, Ex, ship or WHG approvals depending on the model. [3]

Editorial calculation: a 60 VA contact at 120 VAC carries 0.5 A and at 24 VDC 2.5 A, while a 16 A contact at 250 VAC is a 4,000 VA rating; compare these with the pump starter coil or motor current before wiring a load to the switch. [1]

Give the supplier the medium (liquid or solid, conductivity, viscosity, foam, build-up, density), tank type and mounting position, number of switch points and their heights, function (high or low alarm, fill, empty, shut-off), supply voltage and the load each contact switches, enclosure rating and cable or conduit, process connection, wetted materials, temperature and pressure, hazardous-area or hygienic approvals, and quantity.

02

Set up fill, empty and alarm control

Flowline's controllers for level switches take one to three switch inputs and provide automatic fill or empty control with high and/or low alarms (LC40-42, rail mount, one to three SPDT relays), a single high or low alarm (LC10, one SPDT relay) or automatic fill or empty from two switches (LC11, one SPDT latching relay), on 120/240 VAC in NEMA 1 or NEMA 4X housings, some with a strobe alert option. Its controllers for level transmitters add 6-digit or 3.5-digit displays and two to four SPDT relays on 85–265 VAC, 12–24 VDC or 120/240 VAC supplies. [2]

Editorial note: Flowline's two-switch LC11 uses a latching relay; ask any supplier how the pump starts and stops between the two switch points, the failsafe state of each relay on power loss, and how alarms are separated from control points.

03

Compare what suppliers offer

Suppliers linked to this page list level switches or level controllers; each card links to the page reviewed.

Listings include capacitive and RF admittance level switches, tuning-fork and rotary-paddle switches for solids, ultrasonic level switches, water level controllers and refrigeration liquid level switches; ask each for the technology, contact rating, process connection, wetted materials and approvals.

04

Check switch point, hysteresis and delay on a vibrating fork switch

Emerson's product data sheet for the Rosemount 2120 vibrating fork level switch gives, in water, a hysteresis of 0.1 in (2.5 mm) and a switching point 0.5 in (13 mm) from the fork tip when mounted vertically, or from the fork edge when mounted horizontally, and states that the switching point varies with liquid density. [4]

The data sheet sets a minimum liquid density of 600 kg/m³, a viscosity range up to 10,000 cP and a maximum recommended solid particle diameter of 5 mm, with bridging of the forks to be avoided. Switching delay is user-selectable at 0.3, 1, 3, 10 or 30 seconds for dry-to-wet and wet-to-dry switching, which Emerson presents as a guard against false switching from splashing in batch tanks with stirrers and agitators; the switching mode (dry = on or wet = on) is also selectable. Extended forks are listed up to 4,000 mm, and a magnetic test point lets the switch and the system connected to it be function-tested. [4]

Editorial note: these figures cover the switch-point and switching-delay rows that the other reviewed sources leave blank; ask any supplier for these values in your own liquid, since density and viscosity change them.

05

Trace the level control construction

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your tank

A level controller quotation needs values for your application. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the medium, points and loads together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Medium: [liquid or solid; conductivity; viscosity; foam; build-up]
Tank: [type; mounting position]
Points: [number; heights; function]
Outputs: [supply; loads switched; relay or transistor; IO-Link]
Construction: [connection; materials; enclosure]
Approvals: [Ex; hygienic; WHG]
Controller: [fill/empty; alarms; mounting]

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