GESTRA NRR 2-50 Level Controller for Boiler Feedwater Valves

A panel-mount level controller with digital display for boiler feedwater valves

The GESTRA NRR 2-50 is a rail-mounted level controller that works with NRG 21-.. and NRG 26-21 level electrodes or NRGT 26-.. level transmitters as limit switch and water level controller in steam boilers, pressurised hot-water installations and condensate or feedwater tanks. The controller converts the electrode voltage signal or the 4-20 mA transmitter signal into 0 to 100 % of the boiler measuring range and shows the actual value on a four-digit seven-segment LED display. It opens or closes the control valve to hold the setpoint and signals when the preset MIN or MAX limit is reached.

Two types share this data sheet. The NRR 2-50 drives an electrically actuated valve as a three-position stepping PI controller; the NRR 2-51 drives an electro-pneumatically actuated valve as a continuous PI controller with a 4-20 mA manipulated variable output.

Technical specifications

The controller can be configured for fill or discharge control. It must not be used in potentially explosive areas. The data sheet requires an electrically isolated 24 V DC supply meeting double or reinforced isolation standards, and an external T 2.5 A or 1.0 A slow-blow fuse for the output contacts.

When to pick NRR 2-50 or NRR 2-51

Choose the NRR 2-50 when the feedwater valve has an electric actuator with open, stop and closed inputs, and the NRR 2-51 when it is an electro-pneumatic valve with a positioner that takes 4-20 mA. For a transmitter-based system the 4-20 mA input fits a level transmitter, while a conductive or capacitive electrode connects directly. Fitting the panel adaptor lifts the front face to IP 65 so that setpoint and display can sit in a cabinet door. For a CAN bus system with remote display see the GESTRA NRR 2-60; more level products are under level instrumentation.

How the GESTRA NRR 2-50 works

An electrode or a transmitter sends the water level signal to the controller. The controller turns the signal into a value from 0 to 100 percent of the measuring range and shows it. It compares the value with the setpoint. It then opens or closes the feedwater valve to bring the level back to the setpoint.

Where the NRR 2-50 is used

• Steam boilers
• Pressurised hot-water installations
• Condensate tanks
• Feedwater tanks
• Limit switch duty

Selection checklist for the NRR 2-50

• Electrode or transmitter input
• Valve actuator type
• Three-position or continuous output
• MIN or MAX alarm
• Supply voltage
• Relay load
• Analogue output
• Rail mounting space

Installation, commissioning and maintenance notes for the NRR 2-50

Clip the controller onto a rail in the panel. Wire the electrode or transmitter with screened cable. Wire the valve and the alarm contacts. Set the code switch and the setpoint. Press the test button to check the alarm. Protect the settings with a password.

Requesting a quotation for the GESTRA NRR 2-50

Please send the boiler data, the electrode or transmitter type and the valve type. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

NRR 2-50 controller type

It is a rail-mounted level controller with a digital display.

NRR 2-50 output type

It is a three-position stepping PI controller.

NRR 2-50 sibling model

The NRR 2-51 is a continuous PI controller with a 4-20 mA output.

NRR 2-50 sensor inputs

It takes an NRG electrode or a 4-20 mA NRGT transmitter.

NRR 2-50 display

The display is a four-digit seven-segment LED.

NRR 2-50 supply

The supply is 24 V DC and the power use is 2 W.

NRR 2-50 electrode supply

The electrode supply is 12 V DC.

NRR 2-50 relay outputs

It has two volt-free changeover contacts for the valve and one for the alarm.

NRR 2-50 contact rating

The contact rating is 8 A at 250 V AC.

NRR 2-50 analogue output

The analogue output is 4-20 mA with a 500 ohm maximum load.

NRR 2-50 operation

A rotary button with an integrated test button operates it.

NRR 2-50 indicators

Red LEDs show MIN and MAX and amber LEDs show the valve state.

NRR 2-50 fault handling

Faults show as an error code and trigger the alarms.

NRR 2-50 password

The parameter settings can be password-protected.

Boiler level records for the NRR 2-50

Record the setpoint, the alarm tests and any error codes.

Choosing the right NRR 2-50 input

Choose the electrode or the transmitter from the vessel and the water quality.

Documents and quotation

The attached GESTRA data sheet 819207 gives the connection diagrams and the order specification for NRR 2-50 and NRR 2-51. Send the electrode or transmitter type, valve actuator type and boiler type for a quotation, and confirm the variant and approvals before ordering.