B. Murienne - Master Project Thesis - Infoscience - EPFL

-Thermocouple (5SRTC-TT-T-40-36, Omega)
-Relay (DSS41A05, SRC Devices)
-Heating pad 0.5 in × 2 in, 5W/in 2 at 28V (KHLV-0502/5, Omega)
Assembly
For the first temperature and oxygenation setup, the stretcher was simply positioned on a
heating plate heated up to 37ºC and the cardiomyocytes were oxygenated via a superficial flow of
95% O2 and 5% CO2 air. Then, a temperature control system was designed using a flexible
heating pad controlled by a thermocouple via a relay. The corresponding electrical circuit is
represented in Figure 15. The heating pad is attached to the stretcher in order to warm up the
silicone membrane mounted on it, as well as the cultured cardiomyocytes. The thermocouple
senses the temperature of the silicone membrane and modifies the heating pad, in order to
maintain the membrane temperature around 37ºC. If the SSR output generates current because the
thermocouple senses a low membrane temperature, an electric field is created between the coil
and the mechanical switch of the relay, making the switch attracted to the coil. Once the electrical
circuit is closed, the heating pads can heat up. A relay was required as the 8V SSR output was not
enough to directly control the heating pad which at least requires a 12V power supply.
SSR activated
voltage : open
circuit 8V, short
circuit 40 mA
Relay
J1, J2 : alarms
controlling the
SSR output
Membrane
TEMPERATURE CONTROLLER
28
Coil resistance :
500 Ω
Power
supply :
max 28 V
SSR output
Relay
(mechanical switch)
+ -
RELAY
Heating pads
on stretcher
Figure 15. Electrical circuit for the temperature control system [adapted from 60].