Page 17 of 44
TTI-7 Iss.02 – 06/11
CAUTION: When measuring thermocouples with the TTI 7
PLUS
it should be remembered that the temperature may
be read to 0.01
C, and this is equivalent to approximately 0.4
V per digit with a type K thermocouple. Care must
therefore be taken to avoid exposing the instrument inputs to draughts or a heat source such as sun shining on the
front panel. To obtain the best results the instrument should be placed in a temperature controlled room and
switched on for at least half an hour before measurements are made. Running on battery power without the mains
supply connected will also be of benefit. When connected to the mains the batteries will be charged and additional
heat generated inside the instrument. Great care should also be taken to ensure that the correct materials are used
when making connections and avoid unnecessary joints of different materials as these again will cause small errors.
We offer a range of thermocouple connectors for use with the TTI 7
PLUS as
well as a range of automatic reference
junctions and an external reference enclosure with integral Pt100 sensor; please ask our sales staff for more
information.
CALIBRATION
The TTI 7
PLUS
has been designed to give long service and permanence of calibration, together with a low cost of
ownership. Attention to detail in the design stage has produced an instrument that is quick and simple to recalibrate
with the minimum of equipment. Prior to calibration the unit should be placed in a temperature controlled
environment for a minimum of 4 hours. Care could be taken to use good quality test leads, thus avoiding any thermal
emf, together with resistance standards of known value. To select the Cal option, press the MEM key and then
select the Cal option from the menu. The calibration counter number will be displayed. A second menu choice will
be given - Cal or Prt. The Prt option will print the calibration constants to the screen. This is used as a diagnostic
tool to ensure that there is no corruption of these constants. Select the Cal option and you now enter the calibration
routine. The display will ask for a passcode to be entered, the default passcode number is 9252, enter this number
and press OK. The display will then give you the option of changing the passcode to your own personal number, if
you select Yes you will then be asked to enter your chosen number via the keypad ending by pressing OK. Any
number between 0 and 9999 is valid. You will then be asked to confirm your number. Once the new number is
accepted the calibration counter will increment 1. The display will then give a choice of calibration RTD, T/C, RJA,
RJB, it is preferable to calibrate the RTD ranges first.
RTD Calibration
Select this option by pressing RTD. Select Pt100, the display will then prompt you to connect 100 ohm resistance
standard to channel A. When connected press OK and you will be prompted to enter the exact value of the
standard. Once the value is entered and the OK pressed you will be asked to confirm the value by pressing OK again.
The instrument will then calibrate itself against this standard storing the calibration constants in the memory. Next
you will be asked to connect a 400 ohm resistance standard and repeat the above. Finally you will be prompted to
connect a 250 ohm resistance standard and again repeat the above. Once this calibration is completed the display
will return to the main menu. You now have the option to calibrate the Pt25 range. Follow the display instructions
using the 100Ω 25.5 Ω and 62.5 Ω standards.
Thermocouple Calibration
Select this option by pressing the T/C key in the calibration menu. Connect an mV source to the thermocouple input
of channel A using low thermal copper leads and connectors. The display will prompt you to set the input to 0mVdc
and press OK. Next +75mVdc should be supplied and OK pressed. Finally -75mVdc should be supplied and again
the OK pressed. These three values will calibrate the complete thermocouple range of the instrument. The display
will again return to the main calibration screen and the reference junction should now be calibrated.
