3.10. - Temperature Control Macros
te # Read or set the temperature
settemp # Set the temperature
measuretemp # Measure the temperature
showtemp # Show temperature parameters
teramp # Ramp the temperature
Methods for handling temperature control and other
experimental parameters
are likely to vary
greatly from lab to lab and experiment to experiment.
You may be able to modify these standard macros
to suit your specific needs.
The temperature control model assumed by these macros uses
two independent instruments:
one instrument to control the temperature and one instrument
to measure the temperature.
The following global variables are used by the macros:
TEMP_SP |
The set point of the controller in ohms, volts, etc. |
T_LO_SP |
The lower limit for the controller set point. |
T_HI_SP |
The upper limit for the controller set point. |
DEGC_SP |
The temperature from which the set point is derived. |
|
TEMP_CS |
The value of the temperature sensor in ohms, volts, etc. |
DEGC |
The measured temperature. |
The macro below displays the current set point and measured
temperature.
# Display temperature parameters
def showtemp '
measuretemp
printf("Temperature Setpoint = %g (%gC)\n",TEMP_SP,DEGC_SP)
printf(" Measured = %g (%gC)\n",TEMP_CS,DEGC)
'
You must supply the macro
measuretemp. It should read
TEMP_CS from the temperature sensor and convert it to
DEGC. Sample
measuretemp macros are given below.
The
te
macro
is the one you would use most often to display or set the
temperature set point.
# Simple read or set temperature
def te '
if ($# == 1) {
settemp $1
qcomment "Temperature Setpoint at %g" "TEMP_SP"
}
onp; showtemp; offp
'
If invoked without arguments, it simply displays the current temperature
parameters.
Otherwise it invokes the
settemp macro.
The
settemp macro checks its argument against the set point limits and then
calls the
_settemp macro, which you must supply.
# Assign the temperature setpoint
def settemp '
if ($# != 1) {
print "Usage: settemp set_point"
exit
} else {
local _1
_1 = $1
if (_1 < T_LO_SP || _1 > T_HI_SP) {
printf("Temp limits are %g to %g.\n",T_LO_SP,T_HI_SP)
exit
}
TEMP_SP = _1
_settemp
}
'
Here are examples of
_settemp macros from several installations (the symbol
_1 is defined in
settemp): # Write setpoint to a Lakeshore 82C Controller on GPIB bus
def _settemp '
gpib_put(12, sprintf("S%6.4f", _1))
'
# Write setpoint to home-made GPIB device used at MIT
def _settemp '{
local _s
_s = int(32767*_1/10)
gpib_put(4, sprintf("%c%c%c%c\160\200",\
0x80|( _s &0xF), 0x90|((_s>>4 )&0xF),\
0xA0|((_s>>8 )&0xF), 0xB0|((_s>>12)&0xF)))
}'
# Write setpoint to a home-made device used with CAMAC at Harvard
def _settemp '
ca_put(bcd(10000*_1), 0, 0)
'
Here are examples of different
measuretemp
macros:
# Read parameters from a Lakeshore 82C Controller on GPIB bus
def measuretemp '{
local _s
gpib_put(12,"W0")
_s=gpib_get(12)
TEMP_SS=substr(_s,1,6)
TEMP_CS=substr(_s,9,6)*100
RtoT_0 DEGC TEMP_CS
TEMP_SP=substr(_s,17,6)
RtoT_0 DEGC_SP TEMP_SP
}'
# Read setpoint from CAMAC and temperature from GPIB device
def measuretemp '
TEMP_CS = gpib_get(1)/1000
RtoT_0 DEGC TEMP_CS
TEMP_SP = dcb(ca_get(0, 0))/10000
RtoT_0 DEGC_SP TEMP_SP
}'
Keep in mind that
measuretemp is also called at each iteration
of the standard scan macros.
The macro
RtoT_0,
used above,
is one of several in the standard package that convert between
degrees C and kilohms for
common thermistors:
# Temperature to kohms
def TtoR_0 '
local _k # YSI 44011 (100kohm @ 25C) 20 to 120 C
$1 = exp(-11.2942 +5.3483e3 /(_k = ($2) + 273.15)\
-1.42016e5 /(_k*_k) -1.172e7 /(_k*_k*_k))
'
# Kohms to temperature
def RtoT_0 '
local _l # YSI 44011 (100kohm @ 25C) 20 to 120 C
$1 = (1/(+2.2764e-3 +2.20116e-4 *(_l = log($2))\
+2.61027e-6 *_l*_l +9.02451e-8 *_l*_l*_l) - 273.15)
'
(The four parameters in each equation were obtained by fitting a
table of values supplied by the manufacturer of the thermistors.
No guarantees are made about the accuracy of the fitted parameters.)
The following macro will gradually change (or ramp)
a temperature controller to a new
set point.
If the ramp time is greater than 500 seconds, the temperature
is changed every 10 seconds, otherwise the temperature is
changed every 2 seconds.
# Read or set or ramp the temperature
def teramp '{
if ($# == 1) {
te $1
} else if ($# == 2) {
local _i _s1 _f1 _d1 _rtime _stime
_f1 = $1
_rtime = $2
_stime = _rtime < 500? 2:10
_s1 = TEMP_SP
_d1 = (_f1 - _s1) / _rtime * _stime
qcomment "Ramp Temp Setpoint from %g to %g" "_s1,_f1"
for (_i=0; _i<=_rtime; _i+=_stime, _s1 += _d1) {
settemp _s1
measuretemp
printf("Set=%7.4f Meas=%7.4fC\r",TEMP_SP,DEGC)
sleep(_stime)
}
showtemp
} else {
print "Usage: teramp set_point or teramp set_point time"
exit
}
}'
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