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CTR5000 Operating Instructions
62
ASL operating instructions, model CTR5000
4.6
Calibration
It is vital to ensure the CTR5000 is correctly calibrated to obtain the most accurate results.
Good laboratory practice dictates that any instrument should be checked before and after a
day’s measurements.
Note
Regularly check calibration.
The CTR5000 contains a very accurate and stable internal 100Ω reference resistor. The exact
value of the resistor is found by comparing its ratio against a traceable, external 100Ω resistor.
The results of the comparison are used to calculate the value of the internal resistor – i.e. it is
calibrated24. Additionally, the CTR5000 needs other points to ensure that the CTR5000 linearity
specification is met across its full range25. The user calibration values are –
0 Ω, and
100 Ω
A four terminal zero-ohm resistor is required together with a traceable, calibrated resistor for
the 100 ohm point26.
The calibration procedure is simple and is partially automated. The procedure is described in
the following sections.
4.6.1
Calibration menu
From the measurement screen, select
Menu
2 Calibration…
The calibration menu is shown below –
24
It also contains another accurate 100Ω resistor for diagnostic purposes. The value of this resistor is stored when the
instrument is built and used at start-up to check performance at a ratio of 1:1.
25
Yearly recalibration by the agent or supplier is recommended
26
Both available from ASL
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