T° Key - Chauvin Arnoux C.A 6549 Bedienungsanleitung

4.3. / T° KEY
The T° secondary function can be used in two ways. One is to assign a Probe Temperature to an
insulation resistance measurement, the other to refer the resistance to a temperature different from the
measurement temperature.
This makes it possible to observe the insulation resistance over time and judge its evolution under
comparable temperature conditions. This is because insulation resistance varies with temperature
according to a quasi-exponential law.
As part of a maintenance program covering a population of motors, for example, it is important to perform
periodic measurements under similar temperature conditions. Otherwise, the results obtained must be
corrected to refer them to a fi xed reference temperature. This function can do this.
Attention:
 The T° function is not available in the Adjustable Step position.
 If the result of the insulation resistance measurement is out of range ("<" or ">") no temperature
corrected resistance can be calculated.
Procedure:
 You have just made a measurement and have not yet stored it. Make sure that the result is not out
of range, then enter the T° mode by pressing 2nd then T°.
TEMPERATURE
Probe Temperature
Resistance Correction
Rc Reference Temperature
ΔT for R/2
R measured
1.002 MΩ
Rc at 40°C
309 kΩ
 To assign this calculation (or only the Probe Temperature) to the measurement result, press 2nd +
T° again (OK is then displayed).
Remarks:
 During the procedure, pressing the DISPLAY key or turning the switch cancels the modifi cations.
 If the coeffi cient   T used for the calculation is not known, the instrument can calculate it in advance,
using at least 3 stored measurements made at different temperatures (see § 4.5.3)
 Detail concerning the calculation performed:
The insulation resistance varies with the measurement temperature.
This dependence can be approximated by an exponential function:
where Rc: insulation resistance at reference temperature.
RT: insulation resistance measured at T°C (Probe Temperature).
KT: coeffi cient at T°C defi ned as follows:
KT = (1/2) ^ ((Rc Reference Temperature - T) /   T)
with T:
  T: 
Rc Reference Temperature: temperature for which the temperature corrected
 Enter the Probe Temperature at which you made the
measurement (by default, the instrument proposes the value
set in SET-UP).
23°C
 If you want to know the resistance of the probe at another
On
40°C
temperature, set "Resistance Correction" to "On" to perform
10°C
the calculation.
 The calculation is performed immediately and the result is
displayed: Rc.
This indicates what the measurement result would have been
at the reference temperature.
Use the
Rc = KT * RT
temperature at the time of the measurement (Probe Temperature)
temperature difference at which the insulation resistance is halved.
resistance (Rc) is calculated.
84
, , and keys to modify the temperatures.