KROHNE SCU 200: a compact controller for open channel flow, pump control and level signalling

KROHNE has released a new control and signal conditioning unit, the SCU 200, built to sit behind a 4…20 mA sensor and turn its signal into something useful: a local display, totalised volume, relay switching or a pulse output. It's aimed at basic applications where a PLC would be overkill, and it suits water and wastewater work well. Here's what it does, and where it could earn its place.

What is the SCU 200?

The SCU 200 is a compact controller for 4…20 mA field devices, including radar and guided radar level transmitters, pressure transmitters and flow instrumentation. It was released alongside a local display version of the OPTIWAVE 1540 and 1560 radar transmitters, and it's compatible with the whole OPTIWAVE 15xx family, as well as OPTIFLEX guided radar and OPTIBAR pressure transmitters.

The idea is simple. The SCU 200 powers the connected sensor, reads its 4…20 mA signal, and gives you a configurable display plus outputs to act on that signal. KROHNE positions it as a cost-effective alternative to a PLC for basic control tasks, with no separate power supply, control cabinet or relay module needed.

Key features at a glance

KROHNE notes that features and options depend on how each unit is configured, so it's worth confirming that the combination of functions you want can be delivered in a single device.

Open channel flow with the OPTIWAVE 1540

Open channel flow is measured indirectly. A flume or weir creates a known relationship between water level and flow rate, so if you can measure the level accurately, you can calculate the flow.

The OPTIWAVE 1540 is a compact 80 GHz radar with a flush-mounted PVDF lens antenna, HART and Bluetooth connectivity, and commissioning through the OPTICHECK Level Mobile app. Mounted over the flume, it sends the water level to the SCU 200 as a 4…20 mA signal. The SCU 200's integrated volume conversion and totalisers then turn that into flow rate and cumulative volume, shown on site and available through its outputs.

KROHNE presents the pairing as a turnkey replacement for traditional ultrasonic systems. Ultrasonic level sensors depend on the speed of sound in air, which changes with temperature, and windy or fluctuating conditions can disturb the measurement. KROHNE notes that these effects can't be fully compensated for, and over time they can show up as unreliable readings and flow spikes that don't match reality. Radar isn't affected in the same way, and the OPTIWAVE 1540's lens antenna isn't affected by condensation, which helps in damp outdoor channels.

Beyond open channel flow: pump control and other uses

Open channel flow is only one of the jobs the SCU 200 can do. It was designed first as a level and pump controller, and that's where most of its functionality comes into play.

Pump control and pumping stations. With a level transmitter feeding the 4…20 mA input, the three relays can be used for pump control, switching at adjustable levels. This is the classic use in wet wells and pumping stations across water and wastewater networks, where a level signal needs to drive pumps without the cost and setup time of a PLC.

Sewage sumps. KROHNE specifically names sumps as a target application. High-level alarms, pump start and stop, and a local display so operators can see the level at a glance can all sit in one unit.

Level signalling and alarms. With four alarms and relay outputs, the SCU 200 can raise high or low level warnings locally. The display flashes red on alarm, and the relays can be used to drive a beacon or alarm, or to pass a signal on to telemetry or SCADA.

Tank and silo level. KROHNE also lists the display and control of silo and tank levels, using radar, guided radar or pressure transmitters as the level sensor.

Sensors that lack a display or are hard to reach. Because the SCU 200 has its own graphical display, it gives you a readout at a convenient location when the sensor itself is up a shaft, over a channel, or otherwise difficult to access.

Totalising and pulse output. The two totalisers and pulse output give you cumulative volume on site, and a standard pulse signal that a data logger or telemetry system can count.

Sampling. A sampling function is part of the feature set. How it's configured depends on the device configuration, so it's worth asking about if you need it for discharge sampling.

Other 4…20 mA devices. The 4…20 mA input isn't limited to KROHNE's own level range. KROHNE says the SCU 200 can integrate virtually any 4…20 mA device, including flow instrumentation, which means it can also be used to display, scale and switch on the output of an existing sensor.

Things to keep in mind

It's a basic-application controller. Three relays and a handful of alarms go a long way on a pumping station or sump, but complex sequencing across many pumps, or integration into a wider control strategy, still points towards a PLC or SCADA system.

Open channel accuracy starts with the structure. The radar and controller measure level and do the maths. If the flume or weir is poorly formed, silted up or affected by debris, or the radar isn't mounted correctly over the water surface, the flow figure will reflect that. It's also worth confirming which flume or weir types the level-to-flow conversion supports in your configuration.

Set-up is straightforward, but plan the wiring. Terminals are clearly marked and parameterisation is done over USB-C, but the sensor, controller and any downstream logger or telemetry all need to be matched up on signal type and scaling.

Details in this post are drawn from KROHNE's SCU 200 product information and its news release of 9 February 2026.