Input Signals; Output Signals - Danfoss VLT HVAC Drive FC 100 Service Manual

High Power Service Manual for VLT
Adjustable Frequency Drives

2.5.1 Input Signals

The adjustable frequency drive can receive two types of remote input signals: digital or analog.
Digital inputs are wired to terminals 18, 19, 20 (common), 27, 29, 32, and 33. Analog or digital
inputs are wired to terminals 53 or 54 and 55 (common). The terminal functions are set by a switch
found by removing the LCP. Some options may include additional terminals.
Analog signals can be either voltage (0 to +10 VDC) or current (0 to 20 mA or 4 to 20 mA). Analog
signals can be varied like dialing a rheostat up and down. The adjustable frequency drive can be
programmed to increase or decrease output in relation to the amount of current or voltage. For
example, a sensor or external controller may supply a variable current or voltage. The adjustable
frequency drive output, in turn, regulates the speed of the motor connected to the adjustable
frequency drive in response to the analog signal.
Digital signals are a simple binary 0 or 1 which, in effect, act as a switch. Digital signals are
controlled by a 0 to 24 VDC signal. A voltage signal lower than 5 VDC is a logic 0. A voltage higher
than 10 VDC is a logic 1. Zero is open, one is close. Digital inputs to the adjustable frequency drive
are switched commands such as start, stop, reverse, coast, reset, and so on. (Do not confuse
these digital inputs with serial communication formats where digital bytes are grouped into com-
munication words and protocols.)
The RS 485 serial communication connector is wired to terminals (+) 68 and (-) 69. Terminal 61
is common and may be used for terminating shields only when the control cable run between
adjustable frequency drives, not between adjustable frequency drives and other devices. See
Grounding Shielded Cables in this section for correct methods for terminating a shielded control
cable.

2.5.2 Output Signals

The adjustable frequency drive also produces output signals that are carried through either the
RS-485 serial bus or terminal 42. Output terminal 42 operates in the same manner as the inputs.
The terminal can be programmed for either a variable analog signal in mA or a digital signal (0 or
1) in 24 VDC. In addition, a pulse reference can be provided on terminals 27 and 29. Output analog
signals generally indicate the adjustable frequency drive frequency, current, torque and so on to
an external controller or system. Digital outputs can be control signals used to open or close a
damper, for example, or send a start or stop command to auxiliary equipment.
Additional terminals are Form C relay outputs on terminals 01, 02, and 03, and terminals 04, 05,
and 06.
Terminals 12 and 13 provide 24 VDC low voltage power, often used to supply power to the digital
input terminals (18-33). Those terminals must be supplied with power from either terminal 12 or
13, or from a customer supplied external 24 VDC power source. Improperly connected control
wiring is a common service issue for a motor not operating or the adjustable frequency drive not
responding to a remote input.
®
FC Series
MG.90.L1.22 - VLT ® is a registered Danfoss trademark
2 Operator Interface and Adjustable Frequen-
cy Drive Control
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