Resources

1. What is CambridgeIC’s position sensing solution?

For engineers who need to know the position of moving parts in their products, CambridgeIC’s solution precisely measures the position of a target without mechanical or electrical contact.

The moving part is identified with a target, and the position of the target is measured using a sensor built with conventional PCB processes. Positions are calculated by a specialist ICs (known as a CTU - central tracking unit) which can be located away from the sensor and target.

This arrangement means that CambridgeIC’s solutions have a number of advantages:

highly accurate, absolute position measurement
tolerant of misalignment and wide gaps
durable with no performance degradation
can be deeply integrated into product designs to offer significant cost savings

2. How does it work?

CambridgeIC position sensing solutions use resonant inductive position sensing to measure the position of a target. Sensor boards have an excitation coil and detection coils. For each measurement, the CTU drives a short burst of AC current into the excitation coil in the sensor, which in turn generates an AC field. The target attached to the moving part contains a resonator and the AC field will drive the resonator at its resonant frequency.

When the AC current is removed, the resonator will induce decaying EMFs in the detection coils. Their amplitude will vary, depending on the position of the resonator. By reading the amplitude of the EMFs from each detection coil, the CTU is able to calculate the position of the target.

Separating excitation and detection in time gives immunity from stray coupling between the excitation and detection coils. This produces superior sensor performance including more immunity to misalignment.

More details are available in the Technology section and in our CTU data sheets.

3. What is a CTU?

CambridgeIC’s Central Tracking Unit (CTU) chips are single-chip processors for position measurement. They implement the electronic processing for resonant inductive position sensing technology, and support a number of different sensor types, including rotary and linear.

CTU chips measure the position of contactless, inductively coupled targets relative to sensors that are built from printed circuit boards to CambridgeIC’s design.

4. Are CambridgeIC solutions affected by EMC fields?

Generally our solution is not sensitive to other AC magnetic fields as sensor coils are balanced, meaning interference tends to affect both coils equally. The sensor operating frequency is low (around 180kHz). This is higher than motor driver frequencies and their significant harmonics, which explains why we do not have any reports of interference from motors. On the other hand it is much lower than frequencies that typically cause EMC issues, and these are removed with low-pass filters. Detected signal levels are high (typically a volt) so any residual interference is insignificant compared to sensor signals.

5. Are CambridgeIC’s position sensors truly absolute?

Yes, no movement is needed on power up and measurements will be the same before and after power up.

6. Is the solution affected by metal nearby?

We recommend that metals are not in contact with the sensor - a gap of 3mm to aluminium is typically sufficient to avoid compromising performance. Please refer to the relevant sensor datasheet for more on integrating that sensor and its target near metal. For more detail on measuring the effect of nearby metal, and selecting or modifying the nominal target frequency to suit a product’s metal environment, please refer to the “Resonant Frequency Centering” white paper. Please contact us for any additional guidance on integration with metal that is required.

7. Will dirt or moisture affect the position sensor?

CambridgeIC solutions are inherently tolerant of harsh conditions and are insensitive to dirt, shock and vibration. In applications where the sensor may be directly exposed to condensing moisture or immersed in fluids, the sensor and target should be mounted inside a housing. Most sensors can be operated with a big gap to the target, which means it is possible to separately encapsulate the sensor and target. This means there is no need to seal both inside the same enclosure. This in turn means there is no need for sliding seals, which often add considerable cost and complexity when other sensor technologies are used.

8. What is the maximum difference between target and sensor?

CambridgeIC’s solution can allow for quite large and variable gaps between sensor and target. Depending on resolution required, gaps of up to 4mm are possible, allowing space for encapsulation.

9. Can I use it in marine environments?

Yes, we have a number of marine applications including instruments on yachts, submersibles and ROVs.

10. Is a CambridgeIC solution suitable for high volume applications?

Yes, uniquely so, as the sensor design can be deeply integrated into a product, giving both flexibility and cost reduction. Further, much of the manufacturing process for the sensor can be bought in-house, giving control over future prices and quality.

11. How many sensors can be read by a single CTU?

CambridgeIC sells a range of CTU chips, differing in speed and the number of sensors that can be connected. That number depends on sensor Type (see ‘what are the differences between type 1, 2, 4 and 6 sensors?’), as below:


Sensor Category	Basic	Precision
:	Type 1 and 4 sensors	Type 2 sensor	Type 3 sensor	Type 6 sensor
CAM312	2*	1	1	1
CAM502	-	1	-	1
CAM204	Up to 4*	1	1	2

* a CAM204 chip using 3 or 4 basic sensors will require type 1 electronics, otherwise use type 4 electronics

12. What are the differences between Type 1,2,3,4 and 6 sensors?

Sensors can have different number of coils, arranged in several ways, which make them more suitable for some applications than others. We classify these differences in design into types:


Sensor Type	Number of coils		Application
	Excitation	Detection
1 & 4*	1	2	Basic linear and rotary sensing
2	1	2	Long precision linear sensors
3	4		Linear sensors with target freely rotating around measuring direction
6	1	4	Precision linear and rotary sensors

*Type 1 and 4 sensors have different electronics and connections – see data sheets for details.

13. How accurate are CambridgeIC position sensors?

The following table provides performance examples for basic and precision, linear and rotary sensors


	Max Linearity Error	Noise Free Resolution
Basic 25mm Rotary Sensor	±1°	11 bits
Basic 100mm Linear Sensor	±0.25%	10 bits
Precision Through Hole 35mm Type 6.3 Rotary Sensor	±0.2°	13.3 bits
Precision Through Hole 115mm Type 6.6 Rotary Sensor	±0.1°	15 bits
Precision 265mm Type 6.12 Linear Sensor	±0.05%	13.5 bits

Figures are for operation at typical gap including typical installation tolerances. For a specific answer, please select a sensor and view its datasheet.

14. Are there any size limits?

Our sensor designs are for embedding inside products, and sizes reflect this.

The smallest standard rotary sensor is 21mm diameter.

The smallest linear sensor has a measuring length of 5mm.

The largest standard rotary sensor has a diameter of 115mm, with custom designs possible up to about 300mm.

The longest standard linear sensor has a measuring length of 500mm. We have done custom designs up to 2m.

15. How can I test the performance of a CambridgeIC solution?

The simplest way to get started with CambridgeIC solutions is to contact us with your design challenge and we can help you verify which sensor design would be most suitable. Development boards are available for all CTU chips, to help you characterise the performance of our solutions with your product in mind.

To simplify initial evaluation, a CTU Adapter is available to connect any Development Board to a PC over a USB port, and CambridgeIC CTU Software is available as a free download for configuration and viewing and processing measurement results.

16. How can I design CambridgeIC solutions into my product?

CambridgeIC has developed a range of standard sensor designs (including linear, rotary and arc sensors) which can be built using conventional PCB processes by any competent PCB manufacturer. We can supply PCB blueprints for your PCB designer, so sensor designs can be built into a board that can also support other electronic circuitry.

For prototyping we can also supply assembled sensors in low volumes.

17. I have a size/mechanical arrangement that is not covered by the off the shelf designs - can I get a custom design?

Please contact us to discuss