Filter
Top Products
SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES
7-20
Time out calculations using a recommended
9000 and 5000 cycles for temperature and
pressure at the maximum frequency are shown
below.
Time out for temperature: 6,
5.22 = (5.8*10
-6
)(9000/0.01)
Time out for pressure: 16,
15.5 = (3.1*10
-5
)(5000/0.01)
If the time out expires before the requested
number of cycles are read, -99999 is stored in
the input location (Parameter 6). After reading
the correct number of cycles, program
execution advances to the next instruction; the
time out may be over estimated without losing
execution speed.
CONVERTING MICROSECONDS TO °C AND
PSI
The temperature and pressure in microseconds
are converted to °C and psi according to the
following relationships provided by
Paroscientific.
Pressure (psi) =
C * (1 T
0
2
/Tau
2
) * (1 (D * (1 - T
0
2
/Tau
2
)))
Temperature (°C) = Y
1
U + Y
2
U
2
+ Y
3
U
3
where, C = C
1
+ C
2
U + C
3
U
2
(psi),
T
0
= T
1
+ T
2
U + T
3
U
2
+ T
4
U
3
+ T
5
U
4
(microsecond),
D = D
1
+ D
2
U (microsecond),
U = U(t) U
0
(microsecond),
Tau = measured pressure (microsecond),
U(t) = measured temperature (microsecond).
Values for the calibration coefficients (U
0
, Y
1
,
Y
2
, Y
3
, C
1
, C
2
, C
3
, D
1
, D
2
, T
1
, T
2
, T
3
, T
4
, T
5
)
are provided by Paroscientific.
ENTERING THE COEFFICIENTS
Coefficients are entered using CR10 Instruction
30 or 64. A calibration sheet from
Paroscientific which accompanies the
transducer lists the 14 coefficients. Table 7.17-
3 shows the correct format for entering the
coefficients. The coefficients shown are for
transducer Serial Number 30135. Your
coefficients will be different.
TABLE 7.17-3 Coefficient Entry Format for
Paroscientific "T" Series Pressure
Transducer Instruction 30
Coeff. Value Param. 1 Param.
2
U
0
5.860253 5.8603 0.0
Y
1
-3970.348 -3970.3 0.0
Y
2
-7114.265 -7114.3 0.0
Y
3
102779.1 102.78 3.0*
C
1
70.29398 70.294 0.0
C
2
6.610141 6.6101 0.0
C
3
-119.2867 -119.29 0.0
D
1
0.0308837 30.884 -3.0*
D
2
0.0 0.0 0.0
T
1
26.33703 26.337 0.0
T
2
0.8516985 0.85170 0.0
T
3
21.80118 21.801 0.0
T
4
0.0 0.0 0.0
T
5
0.0 0.0 0.0
*Y
3
and D
1
are the only coefficients with a non-
zero exponent.
Only the first 5 digits of each 7 digit coefficient
are entered in the datalogger. The maximum
error that occurs due to using five digit
coefficients is 0.001 psi throughout a 15 psi
range at any temperature between -30 and
+60°C. The maximum error in temperature
calculations is 0.2°C over the same
temperature range.
CONNECTIONS
Figure 7.17-1 details the components required
for connecting the transducer to the CR10. The
user supplied components are commonly
available at commercial electronic stores.
PROGRAM EXAMPLE
The program may be divided into the following
7 steps.
1. Load the coefficients into input locations
(Subroutine 1).
2. Measure the temperature and pressure.
3. Compute U.
4. Compute temperature, °C.
5. Compute T
0
, T
0
2
, Tau
2
, and 1-T
0
2
/Tau
2
.
6. Compute D.
7. Compute C.
8. Compute pressure (psi.)