Chapter 7 – Maintenance
Page 7-10
TestEquity 1016H & 1027H Temperature/Humidity Chamber
Theory of Operation
Overview
Refer to the electrical and refrigeration drawings to identify the referenced items described
below. The electrical items are referenced with a letter(s) and number. The refrigeration items
are referenced with a number only or number followed by a single letter.
Air Heating and Safety Systems
The chamber is heated by an open-element nichrome heater (HT1). The heater is located in the
air plenum. The temperature controller provides a time-proportioned output to the solid state
relays (SSR1, 2). This turns the heater on/off as required to maintain the temperature set point.
Pilot light PL1 provides an indication on the front panel when the heater is on. Fusible heat
limiters (HL) provide failsafe protection against a catastrophic failure by opening the heater
circuit at +240°C. The master heat contactor C1 provides a power interlock for the heaters,
circulator fan motor, and the control system. C1 is controlled by both the Conditioning Switch,
the safety relay (CR1), and the phase control relay (PCR1). CR1 is controlled by the temperature
limit controller (TCR2). If either the high or low temperature safety limits are exceeded, TCR2
turns off CR1, which disables all temperature conditioning functions. PCR1 will disable all
chamber functions if the input power phase-sequence is incorrect.
Humidity System
Water is heated by an immersion-type heater (HT2) to generate vapor. The heater is located in
the humidifier tank. The F4T/F4 Controller provides a time-proportioned output to a solid state
relay (SSR2). This turns the heater on/off as required to maintain the humidity set point. Pilot
light PL4 provides an indication on the front panel when the humidifier heater is on.
Water level in the humidifier is maintained by a float valve assembly which is external to the
humidifier tank.
The immersion heater has an embedded thermocouple which is connected to Input 3 of the
F4T/F4 Controller to control an Alarm output. This provides failsafe protection against a heater
failure in the event of a low water condition by opening the humidifier heater contactor C4 if the
heater r125°C. The alarm will self-reset when the heater r100°C.
