An apparatus, comprising: a thermal chamber; an external heatsink disposed externally to the thermal chamber; an internal heatsink disposed within the thermal chamber; one or more thermoelectric devices thermally coupled to the external and internal heatsinks to transfer heat therebetween in response to a pulse-width modulated power signal; a first temperature sensor disposed within the thermal chamber continuously measuring a chamber temperature; a second temperature sensor coupled to the internal heatsink within the thermal chamber continuously measuring temperature at the internal heatsink; and a feedback control system controlling a duty cycle of the pulse-width modulated power signal in response to a target chamber temperature and real-time temperature measurements produced by the first and second temperature sensors characterised in that the feedback control system includes a chamber feedback control loop in communication with a heatsink feedback control loop, wherein the chamber feedback control loop includes a first controller that calculates the target internal heatsink temperature in response to the target chamber temperature and a real-time temperature measured by the first temperature sensor, and wherein the heatsink feedback control loop includes a second controller, the second controller being in communication with the second temperature sensor as part of the heatsink feedback control loop, the second controller calculating the duty cycle of the pulse-width modulated power signal at which to operate the one or more thermoelectric devices in response to the target internal heatsink temperature received from the chamber feedback control loop and a real-time internal heatsink temperature measured by the second temperature sensor. a thermal chamber; an external heatsink disposed externally to the thermal chamber; an internal heatsink disposed within the thermal chamber; one or more thermoelectric devices thermally coupled to the external and internal heatsinks to transfer heat therebetween in response to a pulse-width modulated power signal; a first temperature sensor disposed within the thermal chamber continuously measuring a chamber temperature; a second temperature sensor coupled to the internal heatsink within the thermal chamber continuously measuring temperature at the internal heatsink; and a feedback control system controlling a duty cycle of the pulse-width modulated power signal in response to a target chamber temperature and real-time temperature measurements produced by the first and second temperature sensors characterised in that the feedback control system includes a chamber feedback control loop in communication with a heatsink feedback control loop, wherein the chamber feedback control loop includes a first controller that calculates the target internal heatsink temperature in response to the target chamber temperature and a real-time temperature measured by the first temperature sensor, and wherein the heatsink feedback control loop includes a second controller, the second controller being in communication with the second temperature sensor as part of the heatsink feedback control loop, the second controller calculating the duty cycle of the pulse-width modulated power signal at which to operate the one or more thermoelectric devices in response to the target internal heatsink temperature received from the chamber feedback control loop and a real-time internal heatsink temperature measured by the second temperature sensor.