02/2014
_____________________________________________________________________________________________________________________
26
6.1.10. Calibration
Calibrate input
Thermocouple
The set of parameters from the MTP200 has to be read in before beginning the calibration. For calibration of
the thermocouple measurement input place the jumpers according to the specifications in the WINSMART
mask for activation of the thermocouple measurement input (see section 10.4 Measurement inputs).
For the 2-point calibration you can freely select the calibration points within the characteristic curve range. In
the case of high accuracy requirements, we always recommend the required measuring range as the
calibration range. Before starting calibration, you have to clarify the question of whether or not to take the
temperature reference junction (TRJ) into account, i.e. should the ambient temperature measured by the TRJ
apply as the reference temperature or 0°C. For calibration with the TRJ you have to mark the box
Take TRJ
into account in the calibration
in the mask.
The calibration procedure begins with simulation of the temperature value for the 1
st
calibration point and entry
of the command
Read in
. The messages
Measurement running
and
finished
appear one after the other in
the mask. After acknowledgement with
OK
the calibration value is accepted and shown analogously as a bar
in the mask. The proportional representation in the bar chart serves as a check and helps to avoid calibration
errors (equal calibration values
equal bar lengths
measured value display not possible
output jumps
back and forth. The same procedure is repeated for the 2
nd
calibration point. Transfer of the calibration values
to the MTP200 marks the conclusion of the calibration procedure. For this mark the box
Overwrite calibration
values
in the main MTP menu, and start the transfer with the button
Program MTP
(see screen area
Interface). The message
Existing parameters will be overwritten.
Still continue
? appears in the mask. Use
OK
to start the process; the next message is:
Transfer parameters
. A last
OK
ends the entire transfer
process and thus the calibration as well.
Temperature reference junction (TRJ)
The TRJ calibration requires a correctly calibrated resistance input as a 2-wire circuit in a
range from 0
– 50 Ω.
The internal TRJ consists of a Pt 100 sensor placed in the terminal block so that the KL19 + KL20 are not
necessary. The terminals KL19 + KL20 are used for connection of an external Pt 100 sensor in a 2-wire circuit
only in the case of an external TRJ. Then you have to use a standard terminal block with the terminals KL17 to
KL20. A more or less substantial error in the cold junction temperature results from the lead resistance of an
internal/external Pt 100 sensor.
There are two options for error correction:
One is to enter the measured resistance value of the lead directly in the mask. The second option is to correct
the sensor error as well as the lead resistance. In this case the read-off TRJ temperature value of the online
mask and a precise measured value of the cold junction temperature are required. You can calculate the lead
resistance for the TRJ calibration via the resistance gradient of the Pt 100 sensor at 0.39
/
C and enter it in
the mask.
Example 1:
TRJ-value
in the online-mask
=
27.40 °C
Measured cold junction temperature
=
22.80 °C
--------------------------------
ΔT = (27,4 - 22,8) °C
=
4.60 °C
Load resistance = 0.39 Ω/°C x 4.6 °C
=
1.79
Ω
