LCDs in Explosive Environments
Q: How can I build an LCD that will be used in an explosive environment?
You may have seen the video of a truck driver refilling the tanks of a gas truck at a gas station. The truck driver used his cell phone as a flashlight to check something close to the opening when the fumes exploded. He was not killed, but the ball of fire threw him several feet in the air. This video brings to question whether a cell phone can ignite gas fumes while filling your car.There is a lot of debate about this and from what I have read, the probability is low, but I don’t want to be the one to test it.
At Focus Display Solutions, we have customers whose products are used in explosive environments such as mines, grain processing facilities, oxygen filled rooms and fueling stations. Their products require a LCD and must operate in such a way as not to generate any type of spark. Although our LCDs do not carry the label ‘intrinsically safe’, we will work with the engineers to modify our display design to reduce the probability of arcing.
A: Some of the possible modifications necessary to decrease the probability of arcing for LCD displays include:
- Reducing the overall capacitive:
LCDs contain several capacitors for use in filtering and improving the response time of the display. Capacitors are small batteries with the ability to quickly discharge and produce an ignition source. It is possible to reduce the capacitor values on the LCD to reduce the potential discharge. Negative side effects include a slower response time of the LCD.
- Increase spacing of board level components:
Electronic components are soldered to the pads on a PCB. Pads that are too close together may produce an arc. It is possible to modify the placement of components on the PCB to increase spacing between key components. Although this does not affect the performance of the LCD, it may require a larger PCB or the addition of layers to accommodate the open areas between components. As a general rule for PCB designs: It is recommended to have one plane for power and a separate plane for ground when designing your product.
- Removal of charge pumps:
Charge pumps, aka “booster circuits” or “bump circuits“, are common on almost all types of LCDs. Their job is to receive a single input and provide multiple outputs at different voltage and current levels. Charge pumps hold the potential of arcing and need to be removed. This means that the LCD may require two or more separate inputs from the customer.