HP 3468A - Page 84

The program shown in the following figure computes the temperature, in °C, cor-
responding to the resistance of a thermistor. The program has been designed to W
work with thermistors exhibiting a 5.000 KQ resistance at 25°C, such as a type
44007 (-hp- part number 0837-0164) or equivalent.
The program gives you the option of selecting either 2-wire or 4-wire ohms
measurements to be made on the thermistor. As it stands, the program sets the
3468A for a 2-wire measurement which gives suitable results if the thermistor is
used at a temperature where its resistance is much greater than the resistance of
the test leads. For greatest accuracy from a thermistor, a 4-wire resistance
measurement should be used. To change to a 4-wire resistance measurement,
delete the exclamation mark from line 50. The program is useful over a
temperature range of —80°C to +150°C.
The coefficients in lines 60, 70, and 80 may be changed for different thermistors.
For example, a thermistor exhibiting 22529 at 15°C - such as a type 44004 -
would have coefficients of: Q1 = .0014684, Q2 = 00023827, and
Q = .00000010112. Consult the manufacturer's data sheet for information on
coefficients.
Lines Description
40-50 Line 40 sets the 3468A to the 2-wire
ohms mode (F3), 30 Kohm range (R3), U
4% digit display (N4), and autozero on
1 PER SuREM
| AEH Spe G4pee THE eHtS (21). Line 50 is used to select the 4-wire
'
-HP-
85
VERSION
ohms
mode.
QUTPUT 981 5 “FSRIN4Z1" . 60-80 These three lines are the resistance to
t
CUSEUT
262
oS
PSRANAZL
temperature
conversion
coefficients
for
the
6A
O3=
aaeeagasd
thermistor.
74 G2=,. G@8@275395
fa
O1=.
G812°86
30
The
REMOTE
9
command
sets
the
inter-
98 REMOTE 9 face at select code 9 to the remote state.
1609 ENTER Sai i B This ensures that all devices in the loop
118
W4=LOGCB>
have
been
autoaddressed
by
the
controller.
128 PHL /COQL+O44(924+04404403 99-27 5 i
Shs 100 Line 100 enters the measured resistance
136
OISP
FP
into
variable
B.
feo a ime 110-120 These two lines perform the resistance to
temperature conversion,
130-140 The calculated temperature is displayed by
line 130. Line 140 causes program execu-
tion to return for another resistance
measurement.
80