We're huge fans of sensors which measure a precise electrochemical value and then output an industry standard 4-20mA control signal.

Our range of 4-20mA control devices includes pH transmitters, Redox Transmitters, toroidal conductivity sensors, dissolved oxygen sensors, turbidity transmitters, ultrasonic level transmitters, and hydrostatic level transmitters - to name just a few!

Significantly the 4-20mA control signal can be transmitted up to 3000 metres away using our LMK2 signal cable and an isolated 4-20mA control signal can be easily incorporated into a PLC, online data logger or any device compatible which can take a 4-20mA control signal.

It's also useful to incorporate a control option to the signal - which is where we offer our range of 4-20mA controllers.

4-20mA Controller Principle of Operation

The key aspect of a 4-20mA controller is that actions or set-points can be triggered based on the incoming signal for a sensor or transmitter.

The 4-20mA control signal is connected to the instrument - this is then displayed on the instruments LCD (liquid crystal display) in either percentage terms (%) or in engineering units which are user selectable with a range of -1999 to + 9999.

With the 4-20mA control signal scaled as required - we also add control functionality to the signal - this means that when the measured value hits a user selected point or set-point, a relay contact can be energised or de-energised. Each 4-20mA controller includes 2 x set-points with corresponding relays.

In addition our 4-20mA controllers include an alarm relay which is energised / de-energised when the control signal is outside of a predefined range and is normally used for switching a beacon, an audible alarm and / or an auto-dialler or remote telemetry device .

4-20mA Controller for Loop Powered Devices

A number of our devices are loop powered devices - this means that the same two wires which transmit the 4-20mA control signal are also used to power the transmitter. This makes connecting a 4-20mA transmitter to a 4-20mA controller or other device incredibly simple - just ensure that the two wires are connected correctly.

When connecting a loop powered 4-20mA device to our range of 4-20mA controllers - the controller provides the power for the 4-20mA device.

The transmission distance of the signal can even be up to 3 km away.

Local Display and 4-20mA retransmission

In addition to powering a 4-20mA loop powered device, our range of controllers also includes a 4-20mA output - this is a retransmission of the incoming 4-20mA signal which can then be looped or cascaded into another device, such as a PLC or building management system.

This is incredibly useful if the 4-20mA controller is located close to the measuring sensor. By having the controller close to the sensor we have a visual display of the measured value on the LCD - which is useful for commissioning, periodic maintenance and any calibration procedures that need to be followed. Especially if we're using the local relays to control dosing pumps or other control devices.

Then if the 4-20mA signal is being connected to a PLC or to a building management system - this signal can be transmitted up to 3000 metres away allowing the sensor to be monitored or data logged via a BMS system.

Easy to use 4-20mA controller

Our range of 4-20mA controllers are simple to use and powerful in functionality. Available in both panel mounting or surface mounting configurations the 4-20mA controllers are precision instruments designed for a long operational lifespan.

4-20mA Controller Range

Ultrasonic Level Transmitters are an excellent way of measuring the liquid contained with a tank or vessel.

The devices are designed to be above the surface of the liquid to be measured, which can include mounting into the top of a closed tank, or on an optional mounting bracket.

Manufactured with an IP67 housing and from chemically resistant materials our ultrasonic level transmitters are designed for to provide accurate and cost effective level measurement solutions on non-foaming liquids, and liquids without a low vapour pressure.

Level Controller Principle of Operation

The instrument is mounted above a tank or vessel using the integral 2" BSP threaded connecting, and must be located at least 0.4 metres above the surface of the solution.

The transmitter is then calibrated to the storage vessel which includes telling the instrument the distance from the surface of the liquid when the vessel is full and the distance to the bottom of the tank. With these parameters inputted into the instrument we can accurately measure the liquid level within the tank.

By transmitting an ultrasonic signal to the surface of a liquid and measuring the amount of time it takes for the signal to be returned, the ultrasonic level transmitter calculates the distance from the surface to the transceiver.

4-20mA Output Signal

The range of ultrasonic level transmitters a micro-processor driven to provide accurate level measurements as well as simple programming and operation.

The levels of the instrument are inserted using a simple array of touch buttons and visualised on an easy to read LCD (liquid crystal display).

The output of the instrument is via an industry standard isolated 4-20mA signal which is easily interfaced with a PLC, online data logger or a from a 4-20mA controller. The output signal can be programmed directly into ultrasonic level transmitter to correspond to the maximum and minimum values contained within the storage vessel.