July 2010 11 – 123
Checking the
PLC outputs
8 You have called TABLE.
8 Press the OUTPUT soft key.
8 Place the cursor on the output to be examined (e.g. GOTO O32 ENTER).
8 Observe the logical state of the output to be checked.
8 Check whether the connected actor (relay, etc.) has triggered or whether the connected
device operates.
8 Measure the 24-V supply voltage DC-link voltage (electrical cabinet voltage).
8 Measure the voltage for the output to be checked, e.g.:
At the terminal strips in the electrical cabinet where the PLC outputs are connected.
Directly at relay terminals, ect.
At the terminals (X4) of the machine operating panel.
At the terminals (X7, X8) of the PL 4xxB input/output unit.
At the terminals (X6) of the input/output module PLD 16-8.
Assignment --> See “Connector Designation and Layout” on page 27 – 447.
Conclusion The logic states in the PLC table must be in agreement with the voltage levels for each
output. --> See “Specifications” on page 11 – 147.
Meaning of the
LEDs on the
PLD 16-8
a. In case of a short circuit of an output, the output voltage is reset.
The short-circuit monitoring remains in place. It can be reset with the manufacturer's
PLC program or by switching the machine on and off.
In order to recognize a short circuit, a current of 20 A must be able to flow for approx. 3 ms.
If this is not the case (e.g. the 24-V supply limits the current sooner), the short-circuit
monitoring might not become effective.
The output voltage for the "1" signal must not be more than 3 V below the measured 24 V
supply voltage (e.g., 22.7 V - 3 V = 19.7 V).
An active output at the PLD 16-8 is indicated by a yellow LED!
A red LED at X4/pin1 indicates a short circuit at the output side of a PLD 16-8.
It is not possible to measure PLC outputs directly at the handwheel or at the cable adapter
for the handwheel!
If the HEIDENHAIN test adapter is available, you can connect it between the connectors
X41 and X46 of the MC to measure the voltage level of the input to be checked. --> See
“Measuring circuit with test adapter for PLC inputs and outputs on the MC” on page 11 –
124.
LED Status Meaning
Red LED at X4, pin 1 Continuously on Short circuit of the outputs
a
Yellow LEDs at X4, X5 and X6 On Inputs/outputs set
Green LEDs at X6, pin 9 and pin 10 On 24 V power supply of the outputs
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