Isotech Comparison Laboratory

NTPL - Isotech's Calibration Laboratory

NTPL - Comparison Laboratory

Lab News: Smaller Uncertainties for the Cal Lab

Uncertainties Lowered, Again!

We have continued to invest heavily in our UKAS calibration laboratories in terms of staffing, training, research and new procedures. As a result we are now able to finalise with UKAS a new schedule with lower uncertainties at the ITS-90 fixed points of Aluminium and Silver. The benefit being smaller uncertainties when we calibrate both ITS-90 fixed point cells and high temperature SPRT calibrations.

Our accredited uncertainties at these points are now smaller than the scope of other accredited laboratories and smaller than most National Measurement Institutes, (NMI) – second only to NIST.

Hydra - Liquid Bath

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Take a Tour: The Comparison Lab

First Stop: TTI 2

The TTI 2 is the ideal 1mK bridge. Can hold calibration data for up to 10 thermometers. Automatically averages up to 50 readings to a resolution of up to 0.000,01°C and calculates the standard deviation. Simplicity itself to use.

Next Stop: Water Triple Point Cells

In the bath are our water triple point cells, the uncertainty for our reference cells is +/-0.000,050°C at 1 sigma, our WTP UKAS accreditation is +/-0.000,070°C. Used here to check our many standard thermometers. SPRT

Next Stop: Gallium Standards

A new plateau - all day, every day. Recently enhanced the Gallium Apparatus Model ITL-M-17401 is now fully automated.

Used to check and calibrate our SPRTs, our watchdog.

Next Stop: Liquid baths

Two models, 814 and 915 (pictured) give use from -80°C to 288°C. Uncertainties to 1mK. Our SPRTS connected to the TTI 2 are used as standards to which the units under test are compared.

Next Stop: Fluidised Furnace

Above 288°C we switch firstly to our Fluidised Calibration Bath Model 875. It circulates aluminium oxide for excellent temperature uniformity, the bath is sealed so the powder stays in the bath. There are no fumes; a problem with high temperature oil and salt baths. Used up to 700°C with uncertainties to +/-0.003°C at 660°C.

Next Stop: Spherical Furnace

For high temperature thermocouple calibration, up to 1300°C, we switch to the Spherical Furnace model 877. Its concentric design gives performance in the order of 0.1°C at 1000°C. A platinum wrap reduces electrical noise and enhances performance.

Std T/C For these temperatures we use our standard thermocouples.
For High accuracy we use an ice point reference for the cold junction. Our Zeref Icepoint Unit, Model 700 is accurate to 0.01°C.

Last Stop

POTTS Along with the full range of comparison baths the Secondary Laboratory also maintains a set of Slim Fixed Point Cells. These cells have been used over the past 10 years during which time the design has been continually improved to offer the smallest uncertainties. But don't just take our word for it, PTB recently compared a set of Slim Cells maintained in Isotech POTTS against their own National Standards. The uncertainties assigned to the the cells in the apparatus is show below.

Slim Cell	Temperature	Uncertainty
Hg	-38.8344°C	0.0015°C
Ga	29.7646°C	0.00025°C
In	156.5985°C	0.0020°C
Sn	231.9280°C	0.0020°C
Zn	419.5270°C	0.0035°C
Al	660.3230°C	0.0050°C

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