Demonstration of Capability
To demonstrate the accuracy and repeatability of ATEX encoder, a stepper motor was programmed to rotate a drive shaft 100,000 cycles in one direction and then 100,000 cycles in the opposite direction, the setup is shown in Figure 2. At one end of the drive shaft was the ATEX encoder and at the other end a COTS encoder. The output from both encoders was collected and reviewed. Both the encoders registered exactly 100,000 cycles at the halfway point and both returned to 0 at the end of the test, see Figure 3, demonstrating equivalence between the two encoders.
The ATEX encoder technical parameters were established through a series of independent studies, one virtual (Ansys) and one physical (TWI), to determine:
- Maximum separation between ATEX encoder and magnetic actuator
- Maximum off-set distance from the centreline of the ATEX encoder and centreline of the actuator magnet
- Maximum off-set angle between the centreline of the ATEX encoder and centreline of the actuator magnet
- Effect of different case materials
The setup for the physical separation investigation is shown in Figure 4 and the results of the modelling are shown in Figure 5. The outcome from both studies agreed within 1%, allowing TWI to replace further physical testing with virtual tests. These results were then used to set the operational parameters of the ATEX encoder relative to the actuator magnet.
It was found that the results from the Ansys Maxwell model matched the practical test results. The good correlation between the model and practical results provided confidence in the modelling and allowed practical experimentation to be replaced by simulation, this significantly reduces the test time whilst extending the number of scenarios that could be investigated. A variety of magnet materials available in Ansys Maxwell with the MDS (Materials Data for Simulation) add-on, allowed the partners to explore the effectiveness of the magnet encased by different materials. Given the anticipated harsh operating environments, selection of the right material was important. Ansys Granta Selector was used to downselect appropriate materials based on durability, cost and supply factors.
The following operational parameters were determined:
- Separation distance between the encoder and magnetic actuator should be < 1.5 mm
- The centre line of the magnet needs to be in line with the recess, should be within 2°
- The case material can be manufactured from brass or stainless steel without compromising the encoder operation
This information was supplied to an independent certification body and the encoder was awarded the designation IECEx BAS 21.0038 (SGS21ATEX0106).