7835
Hydrazine Monitor
2 Introduction
IM/7835–EN Rev. P
5
2 Introduction
2.1 General
The 7835 Hydrazine Monitor uses an electro-chemical cell to
measure the amount of hydrazine in boiler water. The
information provided by the monitor can be used to avoid
expensive overdosing of hydrazine or more costly damage to
boiler plant due to the under-dosing of hydrazine.
The 7835 is an accurate reliable monitor providing trouble-free
operation and requiring a minimum of routine maintenance. It
measures hydrazine over two ranges: 0 to 100 µg kg
-1
and 0 to
1000 µg kg
-1
– the ranges are selected manually or, if required,
switched by the monitor automatically.
The monitor is housed in 2, lockable steel cases consisting of a
liquid handling section (sensor unit) and an electronics section
(transmitter unit). The electronic case is protected to IP55 and
can be separated from the liquid handling section by up to
100m (325 ft).
2.2 Sensor Unit
The liquid handling section contains a constant-head unit
feeding sample to a sensor that can be refurbished. Reagent
solution to raise the pH of the sample is added via a
micro-porous disc. During the calibration sequence, a solenoid
valve blocks the flow of sample that diverts to the drain and
allows flow of the standard solution. Reagent and standard
solutions are held in containers with transparent ends, mounted
inside the sensor unit case.
2.3 Transmitter Unit
Operation and programming of the 7835 is via 4 keys and a
digital display located on the front of the transmitter.
In operation, the transmitter can display measured hydrazine
(µg kg
-1
) and the sample temperature. Set-up of alarm,
retransmission and calibration parameters is achieved in
programming mode, where key parameters are protected by
security codes.
Hydrazine values can be retransmitted to remote equipment
using the retransmission output facility. The values retransmitted
are set automatically to the range selected.
Remote alarm indication is provided by 2 relay outputs. Relays
are programmed to activate when the hydrazine level moves
either above or below a pre-defined trip point.
Remote range indication is provided by 2 relay outputs. The low
range relay is active when the range selected is 0 to 100 µg kg
-1
and the high range relay is active when the range selected is 0
to 1000 µg kg
-1
. In automatic mode the range relays are
activated automatically.
2 Further relay outputs are available to indicate when a
calibration is in progress and if the last calibration failed.
The transmitter unit is provided with 6 cable glands fitted to the
gland plate on the left hand side of the case.
Warning.
Read all relevant sections of this guide before
configuring the system or modifying system
parameters.
Install and use this equipment as detailed in this
guide. Install and use associated equipment in
accordance with the relevant national and local
standards.
System configuration must be carried out only by
users or personnel with approved access rights (user
privileges).
Dimensions in mm (in.)
Fig. 2.1 System Layout
Transmitter unit with door open
490 (19.3)
Transmitter Unit
Sample
Input
Up to 100 m
(328 ft)
Suggested Installation Layout
Sensor Unit
Drain
0216–403 Inlet Valve with
1
/
4
in. Swagelock Fittings
0216–404 Sample Filter with
1
/
4
in. Swagelock Fittings
