Metrohm 774 Oven Sample Processor - Manual (Page 84)

5 Detailed description
774 Oven Sample Processor, Instructions for use 78
FLOW
FLOW
4
>sample sequence
4 FLOW: pump : ON
pump, ON,
valve OFF
Gas flow control
The FLOW command can be used to activate resp. deactivate the pump
(air) or the solenoid valve (inert gas input). The first parameter is used to se-
lect pump or valve.
The flow rate of the carrier gas stream can be controlled in both cases with
the flow controller on the left-hand side of the tower of the 774 Oven Sam-
ple Processor. The flow rate is measured and monitored electronically. If the
limits set in the methods are overshot or undershot, an error message is
displayed.
You should avoid switching on pump and valve since, otherwise, constant
gas flow cannot be guaranteed.
HEATER
5
HEATER >sample sequence
5 HEATER:INIT°C min
INIT, OFF blank
50…250 1…999
Oven control
press <CLEAR> for 'blank'
The HEATER command defines the oven control. The first parameter sets
the target temperature and the second parameter determines the time in-
terval in which the target temperature is to be reached.
A specific value in the above-specified range can be selected for the target
temperature. If you always work with the same temperature, it is advisable
to set an initial temperature to which the system is heated as early as start-
ing in the configuration of the 774 Oven Sample Processor. In the method,
you can then select the initial temperature with parameter 'init'. The oven
heater is switched off if 'off' is the first parameter.
Using the time interval as the second parameter, you can modify the heat-
ing rate in order to program temperature ramps or entire temperature pro-
files (with several HEATER commands). A blank entry for the heating inter-
val results in heating at the maximum possible heating rate (up to approx.
15°C/min in the temperature range <150°C ). Entering a defined heating in-
terval results in slower but controlled heating so that the oven reaches the
target temperature precisely in the specified time. Should it not be possible
to reach the target temperature in the specified time interval (note maximum
heating rate, see above), a HEATER timeout is triggered. In the Parameter
menu, you can define, under '
>Timeout Settings ' (see Page 71) how the
system is to react if a timeout occurs. It is advisable to select a timeout time
(additional time tolerance) of a few minutes.
The HEATER command causes a delay in the method run until the oven
has reached the set target temperature or, if applicable until the timeout has
expired. The next command in the sequence is then executed.