ROTRONIC MBW 373 - Manual (Page 21)

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Heating Time
The Heating Time determines how long to hold at the mirror check temperature before allowing
another dew or frost point measurement. A heating time of 0 results in no hold, meaning that
once the mirror check temperature has been reached, the function ends and dew/frost control
resumes immediately. If a heating time greater than 0 is entered, then the mirror will heat and
remain at that temperature for the duration of the heating time value. Heating time is effective
regardless of whether mirror check was triggered automatically or manually.
Heat To
Edit the Heat To field to change the temperature that the mirror will be heated to, and optionally
held at, during Mirror Check.
Pump Control
The pump, if your system is so equipped, is a diaphragm type driven by a brushless DC motor.
Pump speed, and thus flow rate, is controlled by changing the amount of power applied to the
motor. Pump power can be set from 0 to 100%, accessed through the Pump key of the Control
Setup parameters menu. When connections to the system are made with short tubing of ¼”
diameter resulting in very little flow restriction, settings for pump power of 10 to 25% are often
acceptable. However for long tubing runs, small tubing diameters, or when restrictions are
induced (by externally installed flow meters for instance) higher pump power settings may be
required. Experiment to determine the lowest pump power setting needed to obtain the desired
flow rate. Turn the pump on and off with the fixed Pump key.
Depending on your system configuration, a pump may not be needed. Or if a pump is installed,
it may not necessarily need to be enabled if you are sampling from a positive pressure system.
The pump, if installed, is configured with forward flowing check valves that open easily. This
allows even a slight positive pressure to be used flow gas through the head, even if the pump is
installed but not enabled.
Heater Controls
For the purpose of measuring high dew points, some units are optionally equipped with controls
for heating the measuring head and all internal components in contact with the gas stream. If so
equipped, connections are also available for control of external heated hoses to connect
between the 373 and the device under test.
The head and all internal components are controlled at a common setpoint. A separate control
setpoint is available for the external heated hoses. Both areas may be controlled either at fixed
setpoints, or at some delta temperature above the current mirror temperature, and may be
enabled/disabled independently.
Access to the setpoints, control modes, and enabling is through the Heater key of the Control
Setup menu. The green light indicates whether control is enabled, and whether it operates with
a fixed setpoint or at some delta above the mirror temperature. When no lights are on for a
particular control group, that heater is disabled. It is also possible to run one heater group in a
fixed setpoint mode, with the other running in delta mode. Since the measuring head (and
internal component) heating is completely independent from the heating of the external heated
hose, any combination of control is acceptable. But keep in mind that all components, including
external fittings and interconnects must also remain above the dew point of the gas being
measured to prevent condensation with the tubing.
Once enabled at the desired fixed or delta setpoints, turn the heaters ON of OFF from the fixed
Heater key.
Notes:
1. While it may not be evident from front panel indications, all systems automatically control the
Head Temperature to maintain it at or above 20°C regardless of the on, off, or enabled
status of the heater controls. This is done to prevent the head form cooling to a value that
might allow condensation to form on the external head components such as the cover screw
or optical head.