Berthold LB 134, Руководство пользователя

Страница: 113 / 157

LB 134 7. Probes for the LB 134
103
consumption and ensures a steady gas flow. Three parallel
counting wires ensure a constantly high response probability
over the entire aperture area.
Four spacers keep the detector at a constant distance of 2 mm
from the surface being monitored without coming in contact with
it.
We supply an aperture plate as an accessory which is held in
position by magnets. It is used, for example, to measure finger
tips.
Figure 7.19: The window side of the Tritium probe LB 1239.
The Tritium probe is connected to the basic unit LB 134 using a
spiral cable; the LB 134 automatically identifies the probe after
power on, switches to the CPS mode and takes over the HV
control.
The Tritium probe is a flow-through counter tube using P10 gas
as counting gas for operation (approx. 2000 cm³/min). The
counting gas enters the probe via a transparent PVC tubing and
exits at the window opening, building up a layer of gas between
the contaminated surface and the counting wires which is re-
quired for the measurement. The gas flow is cut off as soon as
the probe is correctly placed onto the console on the trolley.
This turns off the gas flow switch; it is turned on only when tak-
ing off the probe again for another measurement.
7.9.4 Counting Gas Supply
The counting gas used is P10 (gas mixture consisting of 90%
Argon and 10% Methane). A 3-liter cylinder with double pres-
sure reducer is mounted on a small trolley. The gas flows
through a transparent PVC tubing (internal Ø 5mm) to the gas
shut-off valve which opens when the probe is lifted off and clos-
es when it is put down again. From there it flows via the gas
flow meter (rotameter) to the Tritium probe.