1.15 Input Functions¶
Input functions in Safety Simplifier are created in a slightly different way from most other PLCs. All input function blocks in Simplifier Manager (E Stop, Gate, Light Barrier, etc.) are based on the same underlying function. Understanding this function is crucial for understanding the different input blocks in Simplifier Manager. With this knowledge, using the Advanced Input, the user can also create their own custom, application-specific input functions.
An input can be in one of three so-called states: ON-state, OFF-state, or ERROR-state. In OFF-state, the ON output is 0. In the ON-state the ON output is 1. It is important to know that the ON output will only output a logical 1 when the function is in the ON-state. In the ERROR-state, the ON output is 0, and the optional ERROR output is 1.
To better understand how input functions work, first we will look at an E Stop input and see how it behaves.
To start with, notice on the E Stop block that each pin has an OFF-state signal and an ON-state signal (signal types are discussed in 1.15.2 Input signal types). When the correct physical OFF-state signal is received on all terminals of the input function, the input goes to OFF-state. In this state the block outputs a logical 0 (LOW) signal. When the correct physical ON-state signal is received on all terminals of the input function, the function goes to ON-state. In the ON-state, the ON output will output a logic 1. For an E Stop this means that both NC contacts are closed, and the E-Stop is OK. When the E Stop is pressed, the contacts open and pins 1 and 3 read 0 V (open contact), which means all pins receive their OFF-state signal, and the function goes to OFF-state. The ON output now outputs a logic 0 (LOW) signal. The ON output only outputs a 1 when the function is in ON-state. This is true for all safety input functions.
Figure 1.68: An E Stop on pins 2 and 4, where 0V is the OFF-state signal, and VDC is the ON-state signal.
To go to the ON-state, the E-Stop must be pulled out. If both contacts close successfully, the pins will read their ON-state signal, and the function goes back to ON-state. However, if one contact is broken and does not close, one of the terminals receives its ON-state signal while the other receives its OFF-state signal, and the function will go to ERROR-state (due to a multi-channel error). In the ERROR-state, the ON output is 0. If the ERROR output is enabled, it will output a logic 1. The function can never go to ON-state from ERROR-state. It must first receive a valid OFF-state, in this case, 0 V on both pin 1 and 3.
The function will go to ERROR-state for two different reasons: multi-channel errors and signal type errors.
- A multi-channel error means that two input channels differ for too long (one is in OFF-state, and one is in ON-state).
- A signal type error is when, for example, the ON-state signal is configured to be an A-Pulse, but the terminal is receiving a constant high 24 V signal (VDC).
1.15.1 Input States¶
To visualize input states, see Figure 1.69 and Figure 1.72. The E Stop is configured to use terminals 2 and 4. The ON-state signals are VDC for both, so the function expects a high signal (>80% of power supply voltage to the node) to reach ON-state.
Pressing and releasing the E-Stop shows which signals are received on the pins, and how the function switches states. A two-channel error can be simulated by slowly releasing the E-Stop until only one contact closes (see the figures below). The function will go to ERROR-state if the terminal receives the wrong signal for longer than the specified Simultaneity time, which for the E Stop block is set to 500 ms internally.
Whenever the function is in ERROR-state the ERROR output will output a logic 1. Releasing the E-Stop completely after the two-channel error results in both pins receiving their correct ON-state signals again. However, the function does not go to ON-state, because the function has not gotten a valid OFF-state since it was in ERROR-state. Pressing the E-Stop opens both contacts and the function goes to OFF-state. Now, when releasing the button, the function can go to ON-state.
Figure 1.69: E Stop in OFF-state, indicated by all pins being in the OFF position: terminal 2 is receiving 0V, and terminal 4 is receiving 0V.
Figure 1.70: E Stop in ERROR-state, due to a two-channel error in the E-stop function.
Figure 1.71: E Stop with a persistent two-channel error. The function cannot go from ERROR-state to ON-state, even though the correct signals are received on the terminals.
Figure 1.72: E Stop in ON-state (released). Both terminals receive their correct ON-state signal (VDC) indicated by both pins being in the ON position.
1.15.2 Input signal types¶
A signal type defines the shape of the signal the terminal expects. It can be a constantly high (VDC) or low signal (0 V), or a pulse, as described later in this chapter. The signal type defined for a terminal determines if the terminal receives its ON-state signal or OFF-state signal. If the terminal receives a signal that is neither the ON-state signal nor the OFF-state signal, the terminal will indicate ERROR.
On the LED display the terminal states can be seen on the I/O menu. When a terminal is in OFF-state the terminal number LED is red. When a terminal is in ON-state the LED is green. When the terminal is in ERROR-state it is indicated by blinking orange.
Input voltage levels — the signal type does not define the voltage levels that the terminal considers a digital 1 (HIGH) and digital 0 (LOW). The voltage level that is considered a high signal is by default set to 80% of the voltage supply to the unit, and the voltage level that is considered a low signal is by default set to 20% of the voltage supply to the unit. This is so the same program works if the unit is used with any power supply voltage, for example 12 V or 24 V. If a specific voltage is required for a certain input, it can be specified directly on that input (in Volts). For example, the unit could be configured with the default values to consider 80% a high signal and 20% a low signal, but an input can be configured to consider 20 V a high signal and 10 V a low signal. The values specified directly for individual terminals are independent of the supply voltage.
When the input signal goes from low to high or high to low, the logical value is determined based on a hysteresis between the specified voltage values. The signal is logically 1 (HIGH) if the input voltage is above the specified high voltage percentage. The signal goes to 0 (LOW) only when the voltage goes below 20%.
1.15.2.1 VDC¶
The VDC signal is defined as a constant high signal.
1.15.2.2 OSSD¶
The OSSD signal is defined as a constant high signal, where short test pulses are allowed.
1.15.2.3 0V¶
The 0V signal is defined as a constant low signal.
Warning
This signal type must never be used by itself as an ON-state signal, as it cannot handle a disconnection on its own. An input function where one terminal is configured to use 0V as ON-state must have at least one more terminal configured to have an active signal as its ON-state signal type (VDC, OSSD, any pulse signal).
1.15.2.4 A, B, C, D Pulses¶
The A Pulse, B Pulse, C Pulse and D Pulse are unique pulse forms that are uniquely distinguishable between each other. The A/B/C/D pulses must be generated by the Safety Simplifier unit that is using them; thus, they cannot be connected between units.
A short circuit between any normal and inverted A/B/C/D pulses or OSSD is detected by all involved inputs and outputs.
1.15.2.5 Inverted A, B, C, D Pulses¶
The Inverted A, B, C, and D pulses are the exact inverted versions of the A, B, C, and D Pulse described in the chapter above. The pulses must be generated by the Safety Simplifier unit that is using them; thus, they cannot be connected between units.
A short circuit between any normal and inverted A/B/C/D pulses or OSSD is detected by all involved inputs and outputs.
1.15.3 Input properties¶
This chapter describes all the properties that can be changed for an input function. A predefined input function block like E Stop may only use some of these properties. For the Advanced Input function, all the properties are available for the user to change.
1.15.3.1 Enable ERROR Output¶
The Enable ERROR Output property can be changed to enable or disable the ERROR output. The ERROR output goes to 1 whenever the function is in ERROR-state. It is 0 when the function is in OFF-state or ON-state. The ERROR signal can be used in logic for indication, or for setting other functions in safe state.
1.15.3.2 StartUp Test¶
If StartUp test is enabled, the function must get a valid OFF-state before it can go to ON-state after start-up / power on. For example, for a Safety Door, enabling StartUp test means the door must be opened and closed each time the system is started / powered on, to test a complete operation cycle and that all components of the function work as expected.
When the start-up function is selected, it requires OFF-state before ON-state. This means OFF-state will always be required at power on, after loss and return of power, and after loss and return of communication (radio or CAN). For manual hold-to-run devices such as two-hand control, enabling devices, and hold-to-run push buttons, this is a normal requirement to release before activation.
It is normally not needed to activate this for other safety devices such as E-stops and interlocked doors. If start-up is selected for these devices, an E-stop would be required to be pressed and released, and the doors would be required to be opened and closed at power on as well as at loss and return of power/communication.
In other cases, whether to use the start-up function depends on the installation and the risk analysis. For a stop function in a separate Safety Simplifier, a start-up function with a reset can be required in case of loss and return of power/communication.
1.15.3.3 Filter ON (ms)¶
Filter ON means that the inputs need to be in ON-state this amount of time to go to ON-state. The Filter ON property filters the ON-state signal for all terminals in this function, when going from OFF-state to ON-state. The logical signal from this block will be delayed for this time when the function is going from OFF-state to ON-state. This filter does not affect the transition from ON-state to OFF-state or ERROR-state.
The reason for selecting Filter ON is to prevent debouncing contacts from causing ERROR-state. If, for example, one of two contacts debounce, an input block could go to ERROR-state. For push buttons, a recommendation from the producer can be 10 ms debounce time.
Note that filtering is applied to all terminals of the function block. This includes terminals that are configured to use pulsed signals as well. The filter is not applied to the actual physical signal, but to the terminal value itself by the function. When a terminal starts receiving its ON-state signal, the input function it is part of will not consider that terminal to be in ON-state until the Filter ON time has passed.
1.15.3.4 Filter OFF (ms)¶
Filter OFF means that the inputs need to be in OFF-state this amount of time to go to OFF-state. The Filter OFF property filters the OFF-state signal for all terminals in this function, when going from ON-state to either OFF-state or ERROR-state. The logical signal from this block will be delayed for this time when the function is leaving ON-state. For an E Stop this means the reaction time when pressing the E Stop.
Note that filtering is applied to all terminals of the function block. This includes terminals that are configured to use pulsed signals as well. The filter is not applied to the actual physical signal, but to the terminal value itself by the function. When a pin stops receiving its ON-state signal, the input function it is part of will keep considering that pin to be in ON-state until the Filter OFF time has passed.
1.15.3.5 Enable Simultaneity¶
This property enables the Simultaneity property. When disabled, no simultaneity is required on the input. When enabled, the Simultaneity (ms) property can be changed (see 1.15.3.6 Simultaneity (ms)).
1.15.3.6 Simultaneity (ms)¶
The Simultaneity property determines how long two terminals can differ when going from OFF-state to ON-state. If they are in different states for longer than this time, the input function goes to ERROR-state, and waits for a new OFF-state (as explained at the end of 1.15.1 Input States). For a two-hand device, maximum 0.5 seconds is allowed between each hand from OFF to ON-state to fulfil the safety requirement for two-hand devices. The Simultaneity between two or more sensors is also often used for bypassing of light grids when material shall pass into a safeguarded cell.
For other devices, the simultaneity can be useful to detect malfunctions. In an E-stop, if one out of two contacts would have a delayed action, this could be detected before it fails completely.
1.15.3.7 Enable Zero Time¶
This property enables the Zero Time property, which, when enabled, requires the input to be in OFF-state for a certain amount of time before it can go to ON-state (see 1.15.3.8 OFF state min time (ms)).
1.15.3.8 OFF state min time (ms)¶
The OFF state min time property tells the function that the terminals must be in OFF-state for longer than this time before the function can go to ON-state again. This is required whenever the function leaves ON-state, or when the function is in ERROR-state. This property can be used, for example, with a Two-Hand Device input, where the Two-Hand device must be released for at least this time before it can be used again.
1.15.3.9 Comment¶
The Comment property can be changed to add text above the block in the logic graph. This is for giving names or descriptions to blocks and does not affect the compiled program in any way.
1.15.3.10 Inputs¶
This property sets how many channels this input should have. For most applications, Inputs is set to Single (for inputs like Push Buttons), Double (for safety sensors like Gate Sensors or Light Barriers, or for E Stops), or in some cases Quadruple (for example for Two-Hand devices).
For the Advanced Input function, this can be set to a maximum of Octuple (8 channels).
1.15.3.11 Pin Properties¶
Each pin has 3 properties: Pin number, Signal Type ON, and Signal Type OFF. The Pin number property decides which terminal number should be used. The Signal Type ON and Signal Type OFF determine what the ON-state and OFF-state signals should be for this terminal.
Some inputs support specific voltage comparison. Enabling special voltage enables the High Voltage and Low Voltage properties. These determine which voltage levels should be used as a logical high and low signal for this pin. The voltages are independent of the supply voltage.
1.15.3.12 Name¶
It is recommended to give a unique name for every input. Input and output function blocks have a setting Name that can be set by the user to identify the input/output function. The name is displayed on the block in the logic editor. When generating the project report, the input and output identifier names are shown for each function so the user can easily identify the function.
Figure 1.73: A push button with the name "Reset door 1".