Station: Air Heater
of the system
1 shows an air tube with heater and temperature sensor(s). University
College of Southeast Norway, Porsgrunn, has 26 copies of this lab
station, being used in several control courses in both bachelor and
master programmes in technology.
presenting the air heater
mathematical model that has proven to describe quite well the
dynamic behaviour of the outlet air temperature (where one of
the temperature sensors are mounted) in simulations is as follows:
Tenv is the
environmental (room) temperature. It is the temperature in the outlet
air of the air tube when the control signal to the heater has been set
to zero for relatively long time (some minutes).
is the additive contribution to the total temperature Tout
due to the heater. Theat
is given by the following "time-constant with time-delay" differential
= - Theat
[V] is the control signal to the heater.
[s] is time-constant.
[K/V] is heater gain (K is Kelvin, which is the temperature unit
used for temperature increments).
[s] is time-delay representing air transportation and sluggishness of
simulator based on this model a proper initial value of the state
must defined. If you assume that the heater has been turned off for a
while, you can set the initial value to zero.
The parameter values vary somewhat between the
lab stations. However, the following values are typical and can be used
(e.g. in a simulator) unless you have found other values from
Furthermore, you may assume
air heater consists of the following items:
plywood plate on which the devices are mounted
box containing all electrical devices
air fan (originally a PC fan)
potensiomter (variable resistance) for manual adjustment of the voltage
controlling the fan speed.
electric power cable (for connection to mains outlet, e.g. 220 V)
temperature sensors, type Pt100, with measurement signal converter from
resistance to current: INOR miniPack-L
heating element (coil) for electric heating of air. The coil is
originally used in a shoe dryer. Power (assuming 220 VAC) is 250 W.
electrical AC-DC converter from 220 VAC to 24 VDC. Datasheet_power_supply.pdf
Pulse-width modulator (PWM): Carlo Gavazzi RN F23V30. Datasheet_ssr_pwm.pdf
September 2016 by
Finn Aakre Haugen. E-mail Finn.Haugen@hit.no.