Sartorius MC 5, Руководство по обслуживанию, Страница: 25 / 49

Stand 1/94 SARTORIUS MC 5 Balance 25
MC 5
Null Indicator
Checking the Null Indicator:
The null indicator has to be re-adjusted only if the lever does
not stabilize symmetrically between the two beam overload
stops. It is unlikely that the null indicator subassembly will
become mis-aligned on its own.
Checking and Adjusting the Overload Stops:
The upper and lower stops must be adjusted so that the lever
can stabilize symmetrically between them.
When the lever has stabilized, you can measure approx. - 6V at
pin 6 of IC 303 (null indicator output) on the system PCB.
When you move the lever toward the upper and lower stops, the
voltage reading on the digital voltmeter should change by
approx. ± 1 V.
To adjust the beam overload stops, slightly turn the stop screw
as follows:
- lower stop -
adjust the screw located between the null
indicator and the magnet cover
- upper stop -
adjust the screw located on the rear section of
the magnet cover
Adjust the catch pin of the lever in the magnet cover so that the
lever can move freely.
A build-up of dirt on the coil or foreign objects on the null
indicator will cause the balance readouts to be non-reproducible.
Make sure that the stops are clean (no dirt film); if
necessary, use alcohol to clean them.
Preload
Checking the Preload:
With the weighing pan in place, the microbalance, when
unloaded, must generate a voltage reading of - 500mV ±50mV
on the digital voltmeter; at maximum load, it must generate
approx. 6.35V (unidirectional control circuit).
Adjusting the Preload:
Allow the beam to stabilize.
The preload weights (M 1.4 nuts and washers) are secured by
thescrew fastener which is located on top of the null indicator
flag.You can change the preload voltage by adding or removing
the washers.