PRESYS
Instruments
T-650PH
Page 11
To verify the step values of a program, select the
VARIABLE
option and confirm
the values shown in the display with the key
ENTER
. The
10%
,
20%
and
25%
options
change the number of steps automatically and recalculate the values according to
SETPOINT HIGH
and
SETPOINT LOW
.
PRBe
: This option enables the use of an external probe for the dry block
temperature control when selecting
YES
. In order to use the internal probe, select
NO
.
When enabling the external probe, configure the probe calibration parameters in the
PARAM
menu and the temperature unit in
CF
as degrees Celsius or Fahrenheit. The
calibration parameters correspond to the R
0
, A, B, and C coefficients of the
Callendar-Van Dusen
equation:
R(t) = R
0
{1 + A.t + B.t
2
+C.t
3
.(t
– 100 °C)}, C = 0 for t ≥ 0.
This equation is generally used in the IPTS-68 temperature scale, where t
refers to the temperature in this scale and R
0
to the resistance at 0 °C. However, it
can also be used in the ITS-90 scale.
The menu for the configuration of these coefficients is shown below:
R0
A
B
C
E_A
E_B
E_C
To enter the value of a coefficient, it must be split into a mantissa and an
exponent as it is used in scientific notation. For a C coefficient equal to -3.151052×10
-2
,
for example, type its mantissa (an integer and a fractional part with six digits) in the
C
mnemonic and its exponent, as an absolute value, in the
E_C
mnemonic. In this way,
C
= -3.151052 and
E_C
= 2.
Note that the signal can be inverted by pressing the key
ZERO
when the number
on the display is zero. This changes the signal from
+
to
-
, or vice-versa.
The coefficients for the ITS-90 scale according to the IEC-60751 standard are shown
below:
R
0
= 100.00000
A =
+3.908300
E_A = -03
B =
-5.775000
E_B = -07
C =
-4.183000
E_C = -12
MD:
Maximum deviation from the set point for the temperature control with an
external probe. The temperature is stabilized by the control after it enters in the range
limited by
SET ± MD
. This parameter must be configured as 1.0 °C.
SC
: This function scales the input reading. The scaling is very useful in
temperature transmitter calibration, for instance, because it displays the current
temperature and the transmitter reading (mA) in the same unit. Thus, the error can be
verified directly in °C or °F. Select the option
SC
and press
ENTER
. If no input is
selected in
IN
, the calibrator will show the
SELECT
INPUT
FIRST
message. In this
case, go to menu
IN
and select the input signal type.
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