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The QNET HVAC incorporates Microchip 2-Wire High-Accuracy Temperature Sensors model MCP9801. The
complete specification sheet the temperature sensor can be found at
www.microchip.com/downloads/en/DeviceDoc/21909d.pdf.
2.2.3 Power Amplifier
The QNET HVAC circuit board includes a PWM voltage-controlled power amplifier that is used to generate heat by
applying the input voltage to an array of resistors in parallel. It is capable of providing 2 A peak current and 0.5 A
continuous current. The output voltage range to the load is between 0 V and 24 V.
2.2.4 Status LED
The QNET HVAC is fitted with a variety of safety measures that use the Status LED for feedback, see Figure 2.3. In
particular, two digital enable lines (one high, one low) are used to ensure proper system configuration. The system
states are displayed as in Table 2.2. Here, a ∗ indicates any state.
External Power (24 V)
0
∗
∗
∗
∗
24 V
†
: Re-enables amplifier when Temperature is < 80 degC
2.3 Environmental
The QNET HVAC is designed to function under the following environmental conditions:
• Standard rating
• Indoor use only
◦
C to 40
• Temperature 5
• Altitude up to 2000m
• Maximum relative humidity of 80% up to 31
• Pollution Degree 2
• Mains supply voltage fluctuations up to ±10% of the nominal voltage
• Maximum transient overvoltage 2500V
• Marked degree of protection to IEC 60529: Ordinary Equipment (IPX0)
2.4 System Parameters
Table 2.3 lists and characterizes the main parameters associated with the QNET HVAC.
Enable+
Enable-
∗
∗
∗
FALSE
∗
TRUE
∗
∗
∗
∗
TRUE
FALSE
Table 2.2: Status LED states of the QNET HVAC
◦
C.
◦
C decreasing linearly to 50% relative humidity at 40
Fan Stall
Temperature
∗
∗
∗
∗
∗
∗
∗
TRUE
∗
∗ ≥ 90 degC
∗ < 90 degC
FALSE
QNET HVAC - User Manual
Status LED
Amplifier
Red
Disabled
Red
Disabled
Red
Disabled
Red
Disabled
†
Red
Disabled
Green
Enabled
◦
C
8
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