Vaisala SHM40 - Manual (Page 29)

Chapter 3 ____________________________________________ Humidity Measurement in Concrete
VAISALA _______________________________________________________________________ 27
Alternate Sealing Materials
Plastic Tubes
Inserting a plastic tube in the hole is always necessary to ensure that you
are measuring the humidity of the concrete at the desired depth. Vaisala
recommends using the tubes in the plastic tube set (19266HM) since they
provide a seal around the bottom part of the tube with the three thin
ridges around the tube. Sealing the crack between the tube and the hole is
important when a drilled hole is used.
If you use a different plastic tube, provide an equivalent seal around tube.
Rubber Plugs
If you need to use a substitute material for the rubber plugs (233976),
you can use putty, tape, or other plugs of appropriate size to plug the
plastic tube. Do not use hygroscopic materials or thin tapes such as
masking tape.
HMP40S probe includes an integrated rubber plug with the cable, so you
always have a rubber plug available when you leave the probe to stabilize
in the plastic tube.
Protective Covers
The protective covers (19268HM) are not required for measurement
accuracy, but they are recommended for the following reasons:
- They keep the probe cable and the quick connector clean during the
long stabilization period.
- They make the prepared borehole easy to find visually, preventing
accidental interference with the measurement and damage to the
probe.