Parr Instrument 4848B - Manual (Page 11)

4848B Reactor Controller
w w w . p a r r i n s t . c o m 9
Thermocouple burnout protection is included in
each of these controllers. If the thermocouple
should burn out, or if there is a break in the thermo-
couple circuit, power to the heater will be shut off.
In most cases this will cause the controller to show
a “NO CONT” reading. A similar high reading will
be displayed if the controller is turned on without an
attached thermocouple. In either of these situations,
the high limit reset will activate. The thermocouple
break must then be corrected and the High Limit Re-
set must be reset in order to activate the system.
High Limit Reset
Each Series 4848B Controller has a high tempera-
ture limit control which will trip the High Limit Relay
and shut off the heater if the temperature reaches
a preset level. If tripped, the lockout relay will pop
out, thereby preventing the system from heating
the reaction when the temperature falls back below
the limit setting. This must be manually reset before
heating can occur again.
On Model 4848B Controllers the high tempera-
ture limit is preset at the factory to 375 °C for most
systems. On these controllers an alarm condition
is indicated by an illuminated red indicator labeled
as "ALM". If the temperature exceeds the limit, the
controller alarm condition will appear, the High
Limit Reset will be tripped, and power to the heater
will be shut off.
Access to the Controller Cabinet
To open the controller cabinet, unplug the power
cord and remove the two screws in the upper
corners of the back panel. Then lift the top plate
upwards, allowing the hinged top and front panel to
swing forward, providing full access to all internal
components.
Caution!
Inside of controller cabinet should be ac-
cessed by qualifi ed personnel only.
Fuses
The 4848B Controller has a number of fuses which
are intended to be fi eld serviceable.
Fuse Rating Part No.
Instrument
Fuse Fast acting, 1 Amp,
250VAC 139E6
Cooling Fuse Fast acting, .25 Amp,
250VAC
139E10
Line Fuse(s) Fast acting, 20 Amp,
250VAC 2074E
Motor Board
Fuse (A+) Very Fast acting, 8
Amp, 250VAC 959E5
Motor Board
Fuse (L) Fast acting, 10 Amp,
250VAC 185E2
Motor fuse/
reset Check back panel for
specifi cations Check part
list
Caution!
Unplug unit before servicing. For continued
protection against possible hazard, replace
fuses with same type and rating of fuse.