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Replacement for Allen Bradley PLC valve acuators

EMA has experienced great success is using the Bardac Smarty controller to integrate with existing PLC programs, such as Allen Bradley PLC networks, with greatly reduced costs, and better performance.

Recently a long standing customer in the lumber mill business contacted us regarding some valve actuators. These actuators used a 4-20 mA analog signal from an Allen Bradley PLC to proportionally control the amount a valve would open or close. The valves were used to control the heat and humidity inlet to the kiln during the lumber curing process.

The existing analog signal coming from the Allen Bradley PLC went directly to the valve actuator. These particular actuators were becoming more expensive, harder to find and were consistently failing. The lumber mill contacted EMA for a solution to remove the actuators using the Allen Bradley PLC analog output, and instead use one that operated from a 120 volt signal. Obviously sending the analog signal from the Allen Bradley PLC directly to the new 120Vac actuator wasn’t feasible.

Bardac SmartyTo avoid making costly hardware (and software) changes to the Allen Bradley PLC, we elected to use the Bardac Smarty. The model Smarty we used is capable of handling eight inputs and eight outputs. The Smarty is a slim module that can easily be stacked together on DIN rail to provide the required amount of I/O. Programming of the Smarty can be done via an Ethernet and/or a USB port on the front of the module. In this case, three Smarty modules were needed to handle the twenty actuators, ten kilns at two actuators per kiln (one Heat, one Humidity aka “Spray”).

The analog 4-20mA signal from the Allen Bradley PLC was fed to the input channel of the Smarty. Function Block programming in the Bardac Smarty converts the analog signal first to Digital, High or Low, then thru a set of comparators and timers to control a digital output that relays the 120Vac external power to the new actuator for On or Off control. Converting an analog signal to digital is not necessarily tricky or something only the Smarty can do. What the Smarty can do, and do very well, is give you the A/D conversion but also give you the capability to control the A/D conversion. Below is a signal flow diagram screenshot of the Heat Actuator function block in the Smarty.

Smarty Program
Smarty Function Blocks

For example, during the installation of the Bardac Smarty, the Heat in the kiln was under and overshooting by ten plus degrees Fahrenheit. The reason for this was the Allen Bradley PLC inputs, programming, and analog output were taking so long (seconds) to update. By the time the Heat valve was told to close it had already let out too much heat. To solve this, a timer function was programmed to “pulse” the Heat valve open rather than leave it open until the temperature setpoint was reached. The Bardac Smarty would see the analog signal rise to a certain value (programmed into a comparator) then actuate the heat valve for 3 seconds (open) then closed. The Smarty would wait 30 seconds before checking the need for more heat and then either pulse the valve again for 3 seconds or do nothing.

This worked fine for desired temperatures of around 90 to 100 degrees F. The system actually held the desired temperature better, more closely, than the original setup. However, when the kiln was called to maintain a temperature of, say, 140 degrees F the actual temperature was always lagging the setpoint. To correct this the Bardac Smarty programming was adjusted to allow a second comparator circuit watching for a 95% input from the PLC. Once the Bardac Smarty received an analog signal proportional to 95% or above, the Smarty output would remain on solid until the analog signal dropped below 95%. At this point, Bardac Smarty would return to the 3 second pulse routine. Once this was all fine tuned on one kiln, EMA replaced the actuators on all ten kilns using the Bardac Smarty for control.

This application is actually a very basic one for the Bardac Smarty. This is an incredibly sophisticated device, that can handle much more complex functions. However, despite the available complexity, as this example shows, its also excellent for more simple applications.

The cost of the Bardac Smarty, including all the software, is considerably less than upgrading or adding to an Allen Bradley PLC network, very reliable, and much more user friendly. (See a blurb on the Smarty’s even lower cost cousin… the Speedy for use in protocol conversions”)

EMA would be happy to discuss applying the Bardac Smarty to your application. Contact us via any of the methods on the right of this page, or your nearest EMA facility as listed at the bottom.

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