Wx-TERM8 – 8 In, 6 Out Terminal Board

Wx-TERM8 User's Manual#

1. Introduction & Installation#

All I/Os on a Wx100 PLC are made available on a 20-pin, 0.1″ spaced header pins, allowing the signals to be easily connected to a terminal board for quick and simple field wiring as shown in the illustration diagram below.

 

The Wx-TERM8 is the most basic I/O boards that provide screw terminals for the basic 8 digital/analog inputs (PNP or NPN) and 6 digital outputs (NPN). Wx-TERM8 also provides LED indicators for all the on board digital I/Os. Using Wx-TERM8 with Wx100 PLC is the simplest way to get started using the powerful PLC for designing your small machines or sophisticated industrial automation projects.
The Wx-TERM8 is supplied in the form of a PCB and can be installed on 4 standoffs spaced out as follow:

The four mounting holes on the Wx-TERM8 is spaced such that you can easily attach two DIN-rail clips (purchased separately as P/N: DIN-CLIP-SET) using 4 pieces of M3 x 10mm screws (supplied in the DIN-CLIP-SET package) and makes the Wx-TERM8 DIN rail mountable, as shown in the picture below:

2. Physical Wiring Diagram#

Physical Wiring Diagram

Note:

  • In the next few sections we will describe in greater details how the power supply, the digital inputs and digital outputs should be wired to the Wx-TERM8 board.
  • The specifications and programming methods for the analog I/Os are detailed in Chapter 5 and Chapter 6 in the Wx100 User’s Manual. Chapter 6  further shows how the special inputs and outputs such as quadrature encoder, stepper motor driver etc. are mapped to the Wx100 digital I/Os.

 

3. Power Supply Wiring#

a) PLC and I/O Using Same Power Supply

Wx-TERM8 can be powered by a regulated switching or linear power supply between 12V to 24VDC (+/- 5% ripple), and can supply up to 2A current. The same power supply can be used to power both the Wx-TERM8 and the Wx100 PLC.

The power supply to the Wx-TERM8 is normally connected to the bottom left screw terminals marked as “POWER IN” on the Wx-TERM8 as shown in the wiring diagram in the last section. The power supply inputs are in-turn routed by the Wx-TERM8 PCB to all the V+ and 0V terminals adjacent to the INPUT and OUTPUT terminal sections for easy connection to I/O devices. Hence power supply input may also be supplied through these V+ and 0V terminals too.

Note:

Internally, the Wx-TERM8 also routes its power supply (via a reverse blocking diode) to the Wx100 via pin19 and 20 on the ribbon cable. This means Wx100 PLC will receive power even if you don’t connect the power supply cable to the PLC’s own power supply screw terminals. However, we do not recommend you depend solely on this connection to power the Wx100 unless your output loads consume only very small amount of current. This is because If you don’t connect separate wires to the Wx100 power connector, then the total output current that the Wx100 output drivers sink from the 6 output loads can only return to the power supply via the ribbon cable, which has limited current carrying capacity and could lead to overheating if it has to constantly carry large amount of return current.

 

b) Using Separate Power Supplies for the PLC and the Load

If the output loads require higher current (such as driving large DC motors) or the loads draw very high in-rush current when turned on and could dip the power supply to below 9V, then it is recommended that a separate power supply be used for the output load. Note that if you choose to use two separate power supplies, their 0V terminals should be tied together to provide a common ground reference for the two power supplies.

It is recommended that the PLC and Load power supply should be either of the same output voltage or the load voltage should be at a higher voltage that PLC power. If the load voltage is lower than the PLC, the output LED may light up even when the output driver is not energized. This is because the current could flow out of the Wx100 output terminal into the (lower voltage) load power supply, essentially applying a reverse voltage to the load (though it is current-limited by a 10K pull up resistor) and therefore light up the LED. This can be confusing to users even though it would not damage the output driver. Should this happen, you will need to add a series diode to the output terminal to block the output LED currents from flowing through the load and into to the load power.

4. Digital Input Wiring#

To simplify field wiring, the power input (V+ and 0V) that Wx-TERM8 receives via its “POWER IN” connectors are routed by the Wx-TERM8 PCB to the input terminal section.

a) PNP Connection#

All Wx100 PLC digital Input are PNP (current sink) by default. This means that to turn ON the digital input you need to supply it a high positive voltage >=+8V. To turn off the digital input you need to supply it <= +3V.

Input Voltage for Logic 0: Open Circuit or 0 to 3VDC
Input Voltage for Logic 1: +8V to +30VDC

 
Each digital input has a green LED indicator which lights up when the input is turned ON. Connecting to a mechanical switch or push button is extremely simple – it only needs to short the V+ to the IN terminal as shown in (a) below. PNP sensors that are powered from 12 to 24V DC is just as easily connected as shown as (b) in Figure 1.5

b) NPN Connection#

NPN (current sink) sensors work in reverse to PNP sensors in that when it turns ON it will want to pull the input to low voltage, whereas when it turns ‘OFF’ it will either leave the input floating or pull it up to the power supply voltage level.

By connecting the “Pullup” terminal to V+, each digital input in the group (e.g. IN1 and IN2 are in one group, IN3 and IN4 are in another group) will be pulled up to V+ via its individual internal 3.3K 0.5W pullup resistor. This means that by default the digital input is turned ON (the green LED will light up) even if the sensor is not connected or sensor output an OFF state. When the NPN sensor turns ON it will pull the input to low, essentially turning OFF the PLC digital input. This means that the NPN sensor behaves in negative logic to the PLC.

When Pullup is connected to V+:

Input Voltage for Inverted Logic 0: Open Circuit or +8V to +30V
Input Voltage for Inverted  Logic 1: 0V to +3V

 

Fortunately, you don’t have to think in term of negative logic when you write the PLC program. By running the special INVERT_INPUTS command once during initialization of the PLC program, you can force the PLC firmware to invert the logic of specified inputs before processing. This includes the digital I/O scan as well as all interrupt-based input functions such as pulse monitoring and high-speed counter operation:

INVERT_INPUTS ch, n

ch
 Every 16 digital inputs are grouped into 1 channel the same way as is defined by the system variable INPUT[ch]. Wx supports up to 5 digital inputs channel = 16 x 5 = 80 digital inputs.
n bit within the channel to be inverted. Any bit that is a ‘1’ in n will signal to the firmware that the corresponding physical input bit is to be inverted during I/O scan or when it is processed by an interrupt service routine.

E.g. If you are connecting only IN1 and IN2 to NPN sensors and the rest to PNP, that means you should set bit 0 and bit 1 to ‘1’ and the rest to ‘0’. So you should run this command:

INVERT_INPUTS 1, &H0003 ‘ Only inputs 1 and 2 are inverted

If you are connecting first 8 inputs to NPN sensors, then run this command:

INVERT_INPUTS 1, &H00FF ‘ Inputs 1 to 8 are all inverted. Inputs 9 to 16 are not inverted.

 

Note:

  1. Run the INVERT_INPUTS ch, n command as early as possible in your PLC program. Ideally it should be the first statement inside an INIT custom function triggered by a SCAN contact at the first rung of the ladder logic.
  2. An input that belongs to the input group where the “Pullup” signal is connected to V+ can no longer be configured as an analog input. Thus, if you have a system that needs to connect to analog, PNP and NPN sensors we recommend that you configure IN7 to IN16 (if available) as the NPN inputs since these inputs are not configurable to be analog inputs in the first place.
  3. Although the ON/OFF input indicators on the i-TRiLOGI online monitoring screen will show correctly the input state of the input corresponding to its defined logic type (either positive or negative logic), the actual green LEDs of the digital inputs will continue to only light up in positive logic mode (i.e. when the input voltage is > 8V) even if an input has already been configured as an NPN input. This should be clearly stated in the service manual for your maintenance technicians to avoid confusion.

 

5. Digital Output Connection#

a) Wiring Digital Outputs#

To simplify field wiring, the V+ power input that Wx-TERM8 receives via its “POWER IN” connector is routed by the Wx-TERM8 PCB to the output terminal section. This allows user to very easily wire to a typical output load. For example, the following shows how to easily use it to turn on a 12V lamp load. By configuring the digital output as a PWM output you can also control how much power to supply to the lamp and thus control the brightness in software.

The load can really be any kind of DC load as long as the working load voltage is compatible to that of V+ and the load current is < 0.5A continuous. It could be as small as a LED indicator lamp, a solenoid valve, the coil of a 12 or 24V relay or contactor, or a DC motor.

 

All digital outputs are directly programmable in Ladder Logic as well as in TBASIC custom functions. Some programming examples are detailed in “Chapter 3 –Digital I/Os and Internal Relays”

b) Relay Outputs#

If you need to switch output loads of different voltages (including AC load) then you may need to use a relay to provide the galvanic isolation between the load voltage and the PLC power supply. To simplify using relay output, Wx-TERM8 provides solder pads for you to solder up to two Panasonic ALQ relays, as shown in the following diagram.

The contacts of these two relays are routed to the terminal marked “COM, RLY5 and RLY6” as shown in the figure to the left.

Note that soldering these two relays does not give you two additional outputs since the coils for these two relays are driven by output 5 and output 6. You must choose relays whose coil voltage match your power supply. For 12V system, solder a ALQ312 relay and for 24V system, solder a ALQ324 relay. You can purchase these relays from www.digikey.com or any electronic components retailers.

Although the relays, the screw terminals and the PCBs are able to handle in rush current up to 10A, we strongly recommend keeping the steady state current carried by these relays to <= 5A each. If you need to switch high voltage, high current load, then you should consider installing an external contactor whose coil can be driven by either the DC output 5 or 6, or the AC power routed via RLY5 or RLY6 terminals.

Note that Out5 & Out6 can still be used to drive DC load of the same power supply so you could potentially use them to switch 12 or 24VDC ON/OFF indicator lamps while at the same time the relay terminals are used to drive the AC load.

One reason we don’t install these two relays as standard is because once you install the relay you must avoid sending high speed switching current such as PWM or stepper motor controller/driver to the relay coils or it can cause the relay to chatter or buzz and can damage the relay contacts. Hence you should only install the relay(s) if you are really using these two outputs for low speed ON/OFF switching of external loads.

Since output 5 & 6 are fully capable of becoming PWM or stepper motor controller outputs, installing the output relay 5 or 6 will limit their flexibility and hence we elected to leave them as user-installable option.

c) Inductive Loads#

When switching inductive loads such as a solenoid or a motor, always ensure that a bypass diode is connected to absorb inductive kicks, which will occur whenever the output driver is turned OFF. Although all the PLC digital outputs already incorporate either internal diodes or intrinsic Zener bypass diodes to protect the driver, some may only activate when the inductive kick voltage rises above 100V DC. This can result in a large dose of noise being introduced into the system and may have undesirable effects. We recommend using a fast recovery diode such as UF4001 to UF4007 connected as shown in the following diagram to absorb the inductive noise:

 

d) Digital Output Specs#

Output #1 to #6

Output Driver type N-Channel power MOSFET with low rDS < 0.05 Ohm
Maximum Breakdown Voltage 40V
Peak Output Current: 2A
Continuous Output Current 0.5A
Output Voltage when OFF Pulled up to V+ via 3K3 resistor
Output Voltage when ON: < 0.1V @2A
Inductive Back EMF Bypass Yes (Intrinsic Zener)

All digital outputs have red or blue LED indicators on the Wx-TERM8 and Wx-TERM16. The Wx100 PLC employs “sinking” (NPN) type power MOSFET outputs that turn ON by sinking current from the load to the 0V terminal.

Notes:

  1. All 6 digital outputs can be configured as 6 PWM outputs using the SETPWM command (See Chapter 11)
  2. Output 1 to 4 may be configured as a single full-step or half-step stepper motor driver, allowing it to directly drive a small stepper motor (See Section 10.2) .
  3. Each pair of output 1&2, output 3&4 and output 5&6 can be configured as stepper motor controller to supply pulse and directional signals to up to 3 external stepper motor drivers. (See Section 10.3)

 

6. Analog Input Connection#

Wx100 PLC has built-in 6 channels of 12-bit, 0.6V to 5V analog inputs that is pin-shared with digital inputs 1-6.

When the PLC is first powered on input 1-6 defaults to digital inputs. Once you run a ADC(n) command the input #n becomes an analog input. The ADC(n) function returns a 12-bit analog readings from channel n. The built-in analog input is unable to properly read analog input voltage < 0.5V. Hence the range is between about 409 and 4095.

a) Wiring ADC to Wx100 PLC via Wx-TERM8 or Wx-TERM16

With Wx-TERM8 and Wx-TERM16, you simply wire the 0-5V output from an analog sensor directly to any of the input 1-6 and 0V to the Wx-TERM8 0V input and run the ADC(n) command to obtain the analog data.

b) Wiring ADC to Wx100 PLC via Customized Terminal Board

Note that each digital/analog input on a WxTERM-8 and WxTERM-16 incorporates a 20K ohm 1% current limiting resistor in between the input terminal and the signal to the Wx100 ribbon cable connector. The Wx100 has scaled the analog inputs that include the 20K ohm resistors in its calculation.

Therefore, if you design your own terminal board and have designated an input to be analog input, then you need to add a 20K ohm 1% resistor in series with the analog signal.

 

c) Electrical Characteristics

No. of A/D channel 6
Resolution 12-bit
Input Impedance 164.2K ohm

Note that each ADC input channel has an input impedance of 164.2K ohm. Hence to avoid loading effect your sensor need supply at least (5/164200 = 0.03mA) at 5V.

d) Interfacing to 0-20mA and 0-10V Analog Signals

With addition of simple resistors you can easily convert 0-20mA or 0-10V signal to 0 to 5V which can then be measured by the Wx100 analog inputs. Please refer to the following diagrams:

Note: The parallel resistance of the (249+1.37=250.37 ohm) and the internal 164.2K impedance of the Wx-TERM8+Wx100 PLC yields 250 ohm, which is then used to convert 20mA current to 5V.

e) Interfacing to Two-Wire 0-20mA Analog Signals

Many 4-20mA analog sensors only have two wire connections and are designed to be powered by the 4-20mA output current that flows through it. These types of sensors can be interfaced easily to the 0-5V analog inputs of the PLC as shown in the following diagram:

The sensor output will be converted to a 1-5V analog voltage and can be read by the PLC using the ADC(n) statement, which will return readings of between 820 and 4092.