ENVIROMENTAL EFFECT
From the given problem of the pressure transducer, following data are
obtained:
Ø Minimum input range, (Imin) = 0 Pa ;
Ø Maximum input range, (Imax) = 104 Pa ;
Ø Minimum output range at an ambient temperature of 20°C, (Omin) = 4 mA ;
Ø Maximum output range at an ambient temperature of 20°C, (Omax) = 20 mA
;
Ø Minimum output range at an ambient temperature of 30°C, (Omin) = 4.2 mA ;
Ø Maximum output range at an ambient temperature of 30°C, (Omax) = 20.8
mA ;
Considering the pressure transducer takes a linear measurement, the
corresponding values of input (I) and output (O) lie on a straight line. This
ideal straight line connects minimum point having the respective minimum
values (Imin , Omin) to the maximum point having maximum values (Imax , Omax)
and thus forming the following ideal straight line equation:
Oideal = KI + a ;
where,
K = ideal straight-line slope = (Omax - Omin) / (Imax - Imin) ;
a = ideal straight-line intercept = Omin - KImin ;
Now at a standard ambient temperature of 20°C (considering ‘K’ as slope and
‘a’ as intercept’) :
Using the above equations,
K
= (Omax - Omin) / (Imax - Imin)
= (20 – 4) / (104 – 0) [Putting the corresponding values at 20°C)
= 16 / 104
= 0.0016
a
= Omin - KImin
= 4 – (0.0016 × 0)
=4
Now at a standard ambient temperature of 30°C (considering ‘K1’as slope and
‘a1’ as intercept) :
Using the above equations,
K1
= (Omax - Omin) / (Imax - Imin)
= (20.8 – 4.2) / (104 – 0) [Putting the corresponding values at 30°C)
= 16.6 / 104
= 0.00166
a1
= Omin – K1Imin
= 4.2 – (0.00166 × 0)
= 4.2
Now to calculate enviromental sensitivity KI, let ‘II’ be the modifying input i.e.
change in temperature.
So, II = 30 – 20 = 10°C ;
Now, in this case, a1 = a + KIII ;
Therefore,
KI
= (a1 – a) / II
= (4.2 – 4) / 10
= 0.02 mA / °C
Now to calculate enviromental sensitivity KM, let ‘IM’ be the modifying input i.e.
change in temperature.
So, IM = 30 – 20 = 10°C ;
Now, in this case, K1 = K + KM IM ;
Therefore,
KM
= (K1 – K) / IM
= (0.00166 – 0.0016) / 10
= 0.000006 mA / Pa / °C
= 6 × 10-6 mA / Pa / °C
Ans : Hence, the environmental sensitivities are given by:
KI is 0.02 mA / °C ; and KM is 6 × 10-6 mA / Pa / °C ;
HYSTERISIS
Level h cm
0
1.5
3
4.5
6
Output volts h
increasing
0
0.35
1.42 2.4
Output volts h
decreasing
0.14 1.25 2.32 3.55 4.43
7.5
9
10.5 12
3.43 4.35 5.61 6.5
5.7
6.78 7.8
13.5 15
7.77 8.85 10.2
8.87
9.65 10.2
Deviation(Output
volts h
decreasing0.14 0.9
Output volts h
increasing)
0.9
1.15 1
1.35 1.17 1.3
1.1
0.8
From the above table Maximumu deviation=1.35
Maximum voltage output=10.2
The maximum hysteresis as a percentage of f.s.d.=(Maximumu
deviation/Maximum voltage output)*100
=(1.35/10.2)*100=13.23%
0