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FAQ

Here are some common questions answered, please contact us if you’d like more help.

What communications methods can be used?

ITW Switches currently offer MODBUS RS485 as its standard communication protocol or I2C for data outputs on its standalone units. ITW Switches are working on ASCII, RS232, Wiegand, Ethernet, KNX, CANopen & BACnet options.  

Please note the I2C communications is only available on the IoT version not all standalone units

What LED Options are available?

Red and Green are the base colours offered, but these can be programmed to offer either no Illumination or Orange when both illuminated.
Blue and White LEDS are available as a special option as are no LED options.
Key back-lighting is not currently available.

What cable types and sizes can I use to connect to the unit?

Solid wire in the range of 0.14 -0.5 mm2 can be pushed directly into the receiving terminal. To remove the wire the contact has to be opened using a small flat bladed screw driver (0.4mm x 1.8mm).

Stranded wire in the range of 0.2-0.5 mm2 can be used but the receiving terminal needs to be opened using a flat blade screw driver (0.4mm x 1.8mm) or bunching will occur. As with the solid wire the contact has to be opened to remove the wire.

An alternative method for the stranded wire is to use a ferrule over the strands. A selection of suggested ferrules can be seen in instruction manual 9940-106.

What is the power consumption of the unit?

Standard unit – flashing (heart beat mode) – 18 mA (nominal)

Unit fitted with communications units (heart beat mode) – 28 mA (nominal)

Continuous red illumination – 50 mA (nominal)

Continuous green illumination – 75 mA (nominal)

Brightness of the LEDs can be varied with the communications variants but his is achieved using pulse width modulation (PWM) so the difference in current drain is negligible.

How does ITW’s capacitive technology work?

ITW’s Chameleon range of capacitive sensing products use changes in capacitance to detect the presence of a finger on or near a touch surface, as shown in the illustration below. This touch button example illustrates a capacitive sensor replacing an electro-mechanical pushbutton switch. The sensing function is achieved using a combination of hardware and firmware.

Capacitive Touch Finger

When a finger touches the overlay touch surface, it forms a simple parallel plate capacitor with the sensor pad through the overlay. The result is called finger capacitance and is a simplification of a distributed capacitance that includes the effects of the human body and the return path to the circuit board ground within the ITW sensor. We then interpret this touch using an ADC method. A current source generates a linear voltage ramp on a capacitor. This voltage is input to an analogue comparator circuit. The comparator’s output is monitored and a counter increments whenever it transitions from high to low.

The ITW sensor includes firmware with algorithms which convert the sensor capacitance into a digital count, called raw count. The raw count is interpreted as either a TOUCH or NO TOUCH state for the sensor, within the firmware. The numerical value of the raw count is the digital representation of the sensor capacitance, and increases as the capacitance increases. Sensitivity is a measure of how much the output will change for a given change on the input. The sensitivity of the ITW sensor is optimised to give best overall performance in a broad range of conditions. The illustration below shows a representation of the raw count of a sensor in the touched and untouched states.

Capacitive Touch Sense Graph

ITW’s capacitive sensing method uses a switched capacitor circuit on the front end of the system to convert the sensor capacitance to an equivalent resistor. The current measured through the equivalent resistor is converted into a digital count. When a finger is on the sensor, the capacitance increases and the equivalent resistance decreases. This causes an increase in current through the resistor, resulting in an increase in the digital count, which is interpreted as a touch.

Can the unit be operated with gloved hands?

When a finger touches the overlay touch surface, it forms a simple parallel plate capacitor with the sensor pad through the overlay. As the finger approaches the touch surface, the capacitance increases. As increasing finger pressure causes the finger to flatten out against the touch surface, the capacitance increases still further. If gloves are worn, they effectively create a spacer between the touch surface and the finger surface, reducing the capacitance. Thus when wearing gloves it may be necessary to press slightly harder to actuate the sensor. The effect of the gloves on perceived sensitivity will vary according to the material from which the gloves are made and the thickness of the material.

Is the unit susceptible to EMI /RFI?

All ITW capacitive sensing products have been rigorously tested to ensure that they comply with the relevant European standards. Please see the DoC supplied with the product for details.

What communications options are there?

The ITW Chameleon range of capacitive sensing products has communication options available. Currently we offer the following options:

Slave with configurable address using 2 wire RS485 communications based on Modbus protocol. Typical use; secure door access keypad.

Slave with configurable address with integrated pseudo-master transmission capability using 2 wire RS485 communications based on Modbus protocol. Typical use; lighting control switch panel.

Slave with defined address using I2C communications. Typical use; configurable control module linked locally to an I2C master.

NB: I2C communications is only available on the IoT version not all standalone units

Please see the product instruction manual for full details of options available and how to use them. 

How is the unit mounted?

The unit can be flush mounted or fitted to a standard pattress box from the MK range. The unit is supplied with two M3.5 raised countersunk slot screws 25 mm long. The unit MUST NOT be over tightened or this will affect the sensitivity of the capacitive switching. Max torque: 0.25 Nm.

Please do contact us if you have any further questions.