Industrial sensors used for continuous position or process measurement commonly provide output signals in the form of either an analog voltage or an analog current. Both are relatively simple interfaces, but there are things to consider when choosing between the two.
Industrial sensors with current output are typically available with output ranges of 0 to 20 mA, which can be converted to 0-10 VDC by using a 500 Ω resistor in parallel at the controller input. Output ranges of 4 to 20 mA, which can be converted to 1-5 VDC by using a 250 Ω resistor in parallel at the controller input. Although it requires a shielded cable, current output allows use of longer cable runs without signal loss as well as more immunity to electrical noise. It is also easily converted to voltage using a simple resistor. Most, but not all, industrial controllers are capable of accepting current signals.
Industrial sensors with voltage output are typically available with output ranges of:
- 0 to 10 VDC (most common)
- -10 to +10 VDC
- -5 to +5 VDC
- 0 to 5 VDC
- 1 to 5 VDC
One of the main advantages of voltage output is that it is simple to troubleshoot. The interface is very common and compatible with most industrial controllers. Additionally, voltage output is sometimes less expensive compared to current output. With that being said, compared to current signals, voltage signals are more susceptible to interference from electrical noise. To avoid signal loss, cable length must be limited. Voltage output also requires high impedance input and shielded cable.
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In my last blog we reviewed how utilizing IO-Link sensors over analog sensors could be cost effective solution as it eliminates need for all the expensive analog I/O cards and shielded cables. In this blog we will see how IO-Link can effectively integrate your analog sensor- in case you want to retrofit your old sensor or maybe just because the IO-Link version for the sensor is not available.
Just to review few main points:
- Your beloved analog sensor typically requires a shielded cable run from the sensor to the control cabinet. The shielded sensor cables are usually 1.5x- 2x the cost of the standard M12 prox cables that you probably use elsewhere in the system.
- Where to connect the shielded cable? Now, you require analog card (typically 4 channel), which is also expensive compared to digital I/O cards — May be equally expensive as the IO-Link card. But, a 4 channel IO-Link master card could offer lot more compared to the 4-channel analog card. Simply put- your analog card can only take another 3 channels of analog signal where as there are a host of devices that you can connect to the IO-Link master to make your system scalable or future proof – more on this later- I get so excited talking about IO-Link.
In any case, coming back to the point- in general we pay a lot of money to add a single analog sensor in the system. What if we could convert the analog signal to digital (same function that the analog card does), closer to the measurement sensor and get the digital data over a standard prox cable back to the control cabinet or to IO-Link? This way, we can totally eliminate or at least reduce the shielded cable run from sensor to the converter.
Balluff offers this A/D converter module — at Balluff we refer to it as “Hobbit” – it is more like a small adapter that fits directly onto a sensor using the standard M12 fittings. The other side is M12 IO-Link connection to take the data back to the controller via an IO-Link master. This single channel “Hobbit” offers 14 bits of conversion – to ensure you don’t lose data in translation.
If you need more than a single channel, Balluff also offers a 4-channel IO-Link hub, this still utilizes only a single port on the IO-Link master. Now, you have 3 or 7 ports (in case of 8 port IO-Link master), open to connect host of other devices such as digital I/O hubs, valve connectors, SmartLights, RFID, color sensors, Pressure sensors, linear measurement devices and so on…
I hope this blog helps you get little more clarity of many benefits of IO-Link. You can always learn more about the benefits of IO-Link at www.balluff.us/iolink.
On behalf of entire Balluff team, I want to wish you all Happy Holidays and Happy New Year!
Example of a Flexible EOA Tool with 8 sensors connected with an Inductive Coupling System.
Over the years I’ve interviewed many customers regarding End-Of-Arm (EOA) tooling. Most of the improvements revolve around making the EOA tooling smarter. Smarter tools mean more reliability, faster change out and more in-tool error proofing.
#5: Go Analog…in flexible manufacturing environments, discrete information just does not provide an adequate solution. Analog sensors can change set points based on the product currently being manufactured.
#4: Lose the weight…look at the connectors and cables. M8 and M5 connectorized sensors and cables are readily available. Use field installable connectors to help keep cable runs as short as possible. We see too many long cables simply bundled up.
#3: Go Small…use miniature, precision sensors that do not require separate amplifiers. These miniature sensors not only cut down on size but also have increased precision. With these sensors, you’ll know if a part is not completely seated in the gripper.
#2: Monitor those pneumatic cylinders…monitoring air pressure in one way, but as speeds increase and size is reduced, you really need to know cylinder end of travel position. The best technology for EOA tooling is magnetoresistive such as Balluff’s BMF line. Avoid hall-effects and definitely avoid reed switches. Also, consider dual sensor styles such as Balluff’s V-Twin line.
#1: Go with Couplers…with interchangeable tooling, sensors should be connected with a solid-state, inductive coupling system such as Balluff’s Inductive Coupler (BIC). Avoid the use of pin-based connector systems for low power sensors. They create reliability problems over time.
Analog signals have been part of industrial control systems for a very long time. The two most common signals are 0-10V (“voltage”) and 4-20mA (“current”), although there are a wide variety of other voltage and current protocols. These signals are called “analog” because they vary continuously and have theoretically infinite resolution (although practical resolution is limited by the level of residual electrical noise in the circuit).
Measurement sensors typically provide analog output signals, because these electronic circuits are well-understood and the designs are relatively economical to produce. But that doesn’t mean it’s easy to design and build a good-quality analog sensor: in fact it is very difficult to engineer an analog signal that is highly linear over its measuring range, has low noise (for high-resolution), is thermally stable, (doesn’t drift as temperature changes), and is repeatable from sample to sample. It takes a lot of careful engineering, testing, and tweaking to deliver a good analog sensor to the market.
Continue reading “For Industrial Controls, What’s Next After Analog?”
In the world of linear position sensors, analog reigns supreme. Sure there are all kinds of other sensor interface types available; digital start/stop, synchronous serial interface, various flavors of fieldbus, and so on. But linear position sensors with analog outputs still account for probably two-thirds of all linear position sensors sold.
When choosing an analog-output position sensor, your choice generally comes down to analog voltage (e.g., 0 to 10 V), or analog current (e.g., 4 to 20 mA). So which should you choose?
Continue reading “Analog Signals: 0 to 10V Vs. 4-20 mA”