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McLeod Gauges Mercury Based

A McLeod gauge is an absolute pressure standard to which many other vacuum gauges are calibrated.  It will accurately measure the total pressure of non-condensable permanent gases (i.e. hydrogen, nitrogen, oxygen, etc.) in a vacuum system, but will not correctly measure condensable vapors if present.  Many condensable vapors will be condensed during compression of the gas sample in the capillary tube and not contribute to depression of the gauge liquid.

The calibration of the gauge for non-condensables is based upon Boyles’ physical chemistry gas law P1*V1 = P2*V2 and therefore measurement of the volume of the glass bulb and the volume per unit length or bore of the capillary tubes is made with high precision.  It is based upon dimensions during manufacture so that once it is correct, very little can go wrong to change its calibration, and so it can be reliably used as a reference standard.

If condensable vapors may be present while calibrating a vacuum gauge against the McLeod gauge, then a liquid nitrogen cold trap should be used to ensure that only non-condensables are being measured.

We offer a number of types of McLeod gauges and they often vary depending on the pressure range to be measured.

Mercury McLeod Gauges
Catalog Number       Pressure Range    Scale       Hg    
94163-020       0-1mm  .001mm    14ml
94163-021     0-5mm      .01mm     14ml
94163-023       0-15mm .02mm    14ml

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