8
NRG 26-61 - Installation & Operating Manual -
819874-00
Usage for the intended purpose
Use as a safety high-level (HW) limiter and low-level (LW) limiter
The NRG 26-61 level electrode is used in conjunction with the URS 60 / URS 61 safety control unit as a
safety high-level limiter and low-level limiter for pressurised steam and hot-water plants.
■
■
Safety high-level limiters prevent the defined maximum high water (HW) level from being exceeded,
e.g. by switching off the feedwater supply.
■
■
Low-level limiters react when the water drops below the set minimum level (LW), e.g. by
switching off the heating.
Safety notes for use as an LW limiter
■
■
Since the electrode measures continuously using capacitance, the low-level limiter function
of the NRG 26-61 may only be used in combination with a conductive NRG 16-60 level
electrode.
■
■
Always use the NRG 16-60 level electrode as the first low-level electrode.
Additional use as a level control system
In addition, the NRG 26-61 level electrode can be used with an NRR 2-60 / NRR 2-61 level controller for
continuously measuring the water level in pressurised steam and hot-water plants or in condensate and
feedwater tanks.
■
■
In combination with the NRR 2-60 / NRR 2-61 level controller, the electrode can be used as a level
control system with MIN/MAX alarm, for example.
■
■
The limiter functions can be disabled independently and by an infinitely variable measurement signal.
Influences of the test fluid
■
■
The NRG 26-61 level electrode can be used in fluids with different conductivity. However, a con-
ductivity of less than 100 μS/cm has a major influence on the measured capacitance, which is why
recalibration of the measuring range (see page 43) at the operating point* and after a cold start is
extremely important.
* Operating point of the plant, see page 7.
■
■
To achieve the best possible reproducibility and maintain high-quality measurements (see “Technical
data” on page 19), the sensor must be installed in a protective tube (see “Installation examples with
dimensions” on page 29 ff.).
■
■
This is the only way to ensure safe use as a level limiter with a SIL 2 rating at the stated values.
■
■
If the dielectric constant of the test fluid differs considerably from that of the usual water used
(Er = 80), it may be necessary to adjust the measuring frequency. For this, please contact the GESTRA
AG Service department.
Visual display and operation
■
■
Viewing and operation take place using the URB 60 or SPECTOR
control operating terminal.
