Question: a shower system is manually controlled by the person who...
A shower system is manually controlled by the person who is having a shower as shown in Figure 1.
Figure 1 – Schematic of manually control shower system
Several system components are working together:
- The mixer mixes hot and cold water streams to one single stream.
- Hot and cold water supply
- Human sensing.
- Control of the mixer handle is through the brain driving the hand to turn an angle.
The mixer has an outgoing temperature T to angle relationship:
- = angle turned by the motor (rad) (measured from vertical line on the mixer as shown in Figure 2)
- T = water temperature from the mixer (deg C)
- K1 = first order coefficient constant (deg C/rad)
- K2 = second order coefficient constant (deg C/rad2)
Figure 2 – Mixer temperature change according to angle turned
The human sensing component follows a root square relationship:
- Km is a constant
The brain controls the hand with an error message determined from a desirable water temperature value. The error message drives the hand to turn the mixer handle with an angle :
- Kn is a constant
- KB is a constant
- Tm is the sensed temperature
- Td is the desirable temperature
The user’s desirable temperature range is 35oC ± 15oC. The output temperature from the system should be as close to the corresponding set value of desirable temperature. Minor deviation from the set value is acceptable.
Which system parameter set would you recommend?