In a previous two-part Industrial Strength Design post on the Energy Zarr Blog, I discussed some of the challenges with designing for hostile industrial environments. I focused mostly on the thermal and ESD aspects of these designs, which can be extremely challenging. I’d like to continue that thread and provide some additional application challenges and some solutions as well.
Today, the Internet of Things (IoT) is becoming the Grand Unified Network that relies on IP transport and the most ubiquitous physical layer to date – Ethernet. The industrial market is also moving away from proprietary networks and moving toward IP based protocols that rely on Ethernet such as PROFINET and EtherCAT. The requirements for industrial Ethernet physical layer implementations are deterministic latency, which is required for such standards as Precision Time Protocol (IEEE1588-2008) and extended temperature range.
Examples of these type of devices are the DP83848I single-port 10/100 Ethernet PHY or the TLK110 which includes extensive cable diagnostic capability. However, to get the precision required for synchronization found in drive systems requires moving the precision time protocol (PTP) functionality into the physical layer to reduce latency and improve determinism. The DP83640 has this capability built in and can synchronize to better than 10 ns with the master clock source which far exceeds the capability of a software implementation.
Figure 1. IEEE 1588 precision time protocol transceiver application
Another area that can be challenging is driving motors. One of the simplest to control is the stepper motor. Simply energizing the windings in a specific order will cause the motor to rotate (or step) a fixed amount. Typically steppers will rotate roughly 1.8 degrees +/- 3% to 5% per step. That is, they will come within 3% to 5% of where the shaft should be if it were perfect. For some applications, this is not good enough so a technique called sine-cosine micro-stepping is used to provide finer control of the motor.
This technique can quickly complicate driving what was a simple stepper motor application. However, TI has come to the rescue with devices such as the DRV8711, which handles all of the drive control as well as many additional features including stall detection. This device has the ability to control the motion within 1/256 of a step to provide very smooth operation for steppers. In addition, the same device can also drive brushless DC motors.
I covered another area of concern in Part II of the Industrial Strength Design post, which discussed an issue of EMI susceptibility. Most every engineer is familiar with ESD vulnerability that can result in catastrophic failure due to electrical overstress – in short, the device is “zapped” by high voltage discharges.
However, a more subtle susceptibility is to strong RF fields affecting the performance of a semiconductor device. This is most notably experienced when placing a cell phone next to a speaker phone while there is a call in progress. When the cellular phone is communicating with the cell tower, a “buzzing” can sometimes be heard from the speaker phone. This is caused by the cellular RF signals being demodulated by parasitic components within the amplifier chain of the speaker phone.
Now imagine that happening in an industrial control system… this could be seriously bad news. To combat the ever increasing RF pollution that surrounds industrial systems, devices such as the LMV851 family of single, dual and quad EMI hardened op-amps have been developed to mitigate these effects. This is especially critical in sensor applications where EMI can affect offsets and cause invalid readings.
So that’s a quick overview of some helpful hints for your next design destined for harsh environments. I hope this brief post puts some more tools in your drawer for making those industrial designs robust and tolerant to severe environments. Till next time…