The CV20 input remains inactive when a PNP PLC output turns on unless the input is pulled toward COM and its logic is inverted. The FV20 supports native PNP wiring; the CV20 requires the 3.3 kΩ pull-down and inversion method or an isolated interface.
Commissioning decision path
Before anything else, confirm the drive model, control supply arrangement, and PLC output type. The similar terminal names do not make the CV20 and FV20 input circuits interchangeable.
| Check | Reading or condition | Meaning and next action |
|---|---|---|
| Drive nameplate | FV20 | Use the native PNP branch. Select the internal or external 24 V arrangement. |
| Drive nameplate | CV20 | The native interface is NPN. Continue to the adapted PNP branch only after checking PLC output compatibility. |
| PLC output | PNP transistor | The output sources voltage when commanded on. Verify its allowable load current and externally applied voltage limits. |
CV20 input-to-COM voltage |
About 25 V before adding the resistor | This is the internally biased NPN input state. A PNP signal cannot produce the required logic directly. |
- Read the exact model from the drive nameplate; do not select the branch from cabinet drawings alone.
- Confirm that the controller output is PNP, not a relay output or an NPN sinking transistor.
- For an FV20, proceed to native wiring. For a CV20, complete the electrical compatibility gate before connecting the PLC output.
FV20 native PNP branch
The FV20 accepts PNP wiring using either its integrated 24 V supply or an external 24 V supply. No pull-down adaptation or input inversion is required solely to obtain PNP operation.
| Supply arrangement | Required common connection | Confirmation before testing |
|---|---|---|
| Integrated 24 V supply | Install a bridge between COM and PLC. |
Measure continuity across the bridge with power removed. |
| External 24 V supply | Connect the external supply 0 V directly to PLC. |
Measure the external supply polarity and voltage before landing the input conductor. |
COM and PLC are control-circuit terminals; do not treat the bridge as a protective-earth connection. Complete the remaining conductors from the FV20 terminal diagram for the selected supply arrangement. Do not move on until an on command produces a high level at the selected digital input relative to its configured control common and the drive input indication follows that state.
CV20 adapted PNP mechanism
The CV20 digital interface is natively NPN. Its input is internally biased high; approximately 25 V was present before loading in the described installation. A 3.3 kΩ resistor from an input to COM pulls the terminal low while the PNP output is off. Inverting that input changes the resulting logic relationship: pulled low means inactive, while the PLC-sourced 24 V means active.
| PLC command | Physical input state | State after inversion | Result for X1
|
|---|---|---|---|
| Off | Approximately 4–6 V with the 3.3 kΩ resistor | Inactive | No Forward command |
| On | Approximately 24 V from the PNP output | Active | Drive starts when X1 is assigned Forward and other permissives are satisfied |
The two reported low-state observations were approximately 4 V and 6 V. Treat that range as a commissioning reference, not a universal switching threshold. Read the actual input voltage and confirm the logical state on the drive. If the terminal remains logically high, stop and check resistor value, the COM connection, and the selected inversion.
At 24 V, the added resistor alone draws I = V/R = 24/3300 = 7.27 mA. At 6 V it carries about 1.82 mA; at 4 V it carries about 1.21 mA. Include the 7.27 mA pull-down load when checking the PLC output rating.
Electrical compatibility gate
The drive can place voltage on the input conductor while the PLC output is off or unpowered. A transistor's internal junctions and protection paths do not grant permission to apply an external voltage to its output terminal.
- Read the PLC output module specifications for continuous source current, off-state leakage, allowable externally applied output voltage, reverse current, and behavior when controller power is absent.
- Add the resistor current to any current taken by the drive input. The known resistor component is approximately 7.27 mA at 24 V.
- With the PLC conductor disconnected, measure the CV20 input voltage relative to
COMwith the drive energized and the pull-down installed. The expected installation reading is approximately 4–6 V. - Determine what voltage and current would reach the PLC terminal when the PLC is off and when it is unpowered. Compare both cases with the module limits.
- If the data sheet does not authorize those conditions, install a properly rated isolated interface or use an NPN output. Do not validate the connection from a low current measured on a different controller.
CV20 configuration procedure
- Remove control power and connect one 3.3 kΩ resistor between the first required CV20 input and
COM. Fit one resistor for every PNP-operated input. - Connect the compatible PNP output to that input. Start with
X1so one channel can be proved before duplicating the circuit. - Set
A6.13to invert the required input. Value0applies no inversions,1inverts onlyX1, and3invertsX1andX2. - For combinations involving
X3orX4, read the exactA6.13selection from the drive documentation. Do not extrapolate an undocumented value. - Confirm that each inverted input has its own 3.3 kΩ resistor. Inverting an unmodified input can create an unintended active command.
- Verify the assigned drive function for each terminal before enabling motion. For the demonstrated
X1mapping, the active state commands Forward.
Final functional verification
- Command the PLC output off. Measure from the input to
COM; the adapted CV20 input should be approximately 4–6 V and its logical indication must be inactive. - Command the output on. Confirm approximately 24 V at the input, an active logical indication, and the assigned command response.
- Remove the command and verify that the input returns inactive. A terminal that remains active points to the wrong
A6.13selection, a missing pull-down, a common-reference fault, or PLC leakage. - Repeat the off/on/off test independently for every modified input. Watch for unwanted simultaneous functions caused by an incorrect inversion combination.
- Test the relevant PLC-off, drive-off, and restoration sequences. Do not release the circuit until no backfeed condition exceeds the PLC output specification and every command returns inactive after removal.
FAQ
Why does a CV20 not start from a PNP PLC output?
The CV20 has a native NPN input interface. Adapt a required PNP channel with a 3.3 kΩ resistor to COM and invert that channel through A6.13.
Why does the CV20 input need inversion?
The resistor makes the PLC-off state physically low, while the PNP output makes the on state approximately 24 V. Inversion maps that low state to inactive and the 24 V state to the requested drive function.
Why does the pulled-down input measure 4 V or 6 V instead of 0 V?
The drive's internally biased input continues to source current through its input circuit and the 3.3 kΩ resistor. Confirm the logical indication rather than demanding exactly 0 V.
Why can voltage at an off PLC output be a problem?
The energized drive may apply voltage to an output terminal while the PLC is off or unpowered. Accept the circuit only when the module specifications permit the resulting external voltage and reverse current; otherwise use isolation.
How do I verify CV20 PNP control before commissioning?
Prove each channel off/on/off: approximately 4–6 V must indicate inactive, approximately 24 V must indicate active, and removing the command must return the assigned function inactive.