We’re contemplating a switch to machine-mount I/O from cabinet-mount I/O for some areas of our larger printing presses. We know that machine-mount I/O is more expensive, but we think we can make up some of the difference because we won't have to design, purchase and install remote I/O cabinets. Are there any other savings from using machine-mount I/O as opposed to conventional cabinet-mount I/O? Are there any safety or other issues that we should be aware of before we make the switch?
—From February '10 Control Design
Significantly Less Costly
In our experience, machine-mounted I/O is significantly less costly than cabinet-mounted solutions, especially if they are used with a suitable low-cost networking strategy. For example, based on list pricing, a four-input AS-Interface IP68/69K machine-mounted I/O module is just $2 more than the equivalent IP20 enclosure-mounted module.
It is absolutely correct that additional savings can be realized because the installation is much simpler and requires less ancillary materials. In fact, machine-mounted I/O has the potential of additional savings when a networking solution with a high degree of granularity is chosen. In this case, the number and length of sensor cables can be reduced.
For machines with low I/O density, "single piece" modules with the "connect and done" technology are available. These types of modules do not even need additional cord sets. Another advantage of using "connect and done" technology is that such modules might make mounting in the conventional sense completely unnecessary.
Helge Hornis, manager intelligent systems,
Not for Everyone
There can be significant savings when switching to machine-mount I/O, but it's not the answer for every application. Machine-mount automation products and I/O are a good fit for applications that include several pieces of modular equipment that need to share intelligence over a long distance. In many cases, printing press lines, with their often extensive in-feed and discharge associated equipment can benefit from machine-mount automation products, depending on their configuration.
One area where machine-mount components provide substantial savings is in the wiring and associated labor cost. On machines that traditionally use a cabinet-bound centralized control system, each sensor or actuator must be wired back to the control cabinet in conduit or cable tray. With machine-mount devices, sensors and actuators can be locally connected to machine-mount I/O. This I/O can either be connected to a local machine-mount controller or connected back to a central controller. Additionally, cabinet-bound automation components inherently require extra troubleshooting steps, often to gain internal cabinet access while complying with plant safety procedures.
In either case, the connection back to the central controller from the local machine-mount I/O or the local machine-mount controller can be made via a wired or wireless network. If the network is wired, just one cable is required for connection of many I/O points back to the central controller. If the network is wireless, then no wiring is required back to the central controller. This approach saves machine builders the costs to design, purchase, install and commission extensive cable and wiring systems. Commissioning costs are usually very high when many I/O points are wired back to a central controller and relatively much lower with the reduced wiring of a decentralized control system.
Paul Ruland, product marketing, automation systems,
Siemens Industry, www.industry.siemens.com
Cutting the Cable
With machine-mount I/O, the sensor cable lenghts are drastically reduced and can be connectorized at both the sensor end as well as at the I/O point right next to the sensor. Although a cable with connectors at both ends is more expensive in general than one with a connector at only one end, it's important to consider the benefits. The sensor cable running back to a main panel is usually 10–100 ft long. A cable that's connectorized at both ends between a sensor and a machine-mounted I/O module can be as little as 0.5 m long, or shorter is some cases. That's an impressive reduction in expensive shielded cable for analog I/O or in multiconductor, non-shielded cables for digitals.
As an added benefit, machine-mount I/O modules are out in plain sight where even an untrained operator can look at the inputs and directly note if a photo sensor, proximity switch or any other input sensor is really working. In the past, when those same inputs had to go back to an electrical panel, it was taboo for an operator to open any electrical panel door. Even knowing where to look in the panel to note the status of a sensor was an issue. Today, troubleshooting has become so simple that the operator can quickly note what equipment on the machine is not functioning. When the operator notifies maintenance, they can accurately suggest what might be wrong and the electrician already knows what to focus on and can possibly even bring required replacement parts in advance. Replacement of parts is fast and easy because with machine-mount I/O, everything is plug-and-play between the I/O module and the sensor.
In this scenario, all the conduit material and wire running from the individual sensors back to the main panel also go down in cost. With machine-mounted I/O, only the communication cable and DC power are needed to run the I/O on the machine.
When it comes to concerns about safety, the old adage holds true—location, location, location. Consider: What nearby equipment could potentially fall onto the machine-mounted I/O? Is the machine-mounted I/O going to get washed down? Water might be OK and not harm the I/O modules, but some aggressive cleaning solvents might cause damage. Is the location of the machine-mounted I/O such that if an operator has to climb on the machine they could step on or trip over the I/O or cables and rip the equipment apart or possibly lead to a workplace injury? Of course, proper precautions and safety considerations should be made with these questions in mind.