Application Example #1:

A high and low alarm light is required for a small tank containing water. There are M12 threaded fittings in the tank for an outside mounted switch located in both the high and low level location. The intent is to have two ALARM LEDs mounted on a panel near the tank. The water temperature ranges from 60ºF to 90ºF. The tank is not pressurized. There is 24 Vdc available for the power.

The Optical Switch selection steps would be as follows:

1. Check to see if the Viscosity of the liquid to be measured is less then 2,000 cP. Water is 1 cP and will work very well with all our optical switches.
2. Check the housing material compatibility for use with water. All three materials will work.
3. Check the pressure requirement. The tank is not pressurized so all three materials will work.
4. Check the operating temperature. All models will operate within the 60ºF to 90ºF range.
5. Select the mounting type. The mounting is an outside mount with a M12 thread. The optical switch choice will now narrow to only those models available with the M12 thread for outside mount.
6. Choose the material of the optical switch. Since all of the basic environment conditions can be handled by all of our material choices. I would recommend the lower cost selection. Which would be a polysulfone housing. Our choice is now limited to only those models with a polysulfone housing and M12 thread for outside mount.
7. Choose the correct input and output electrical specifications. The input power is available is 24 Vdc. For the output, each switch will need to drive an LED. Most bright LEDs will require 20 mA of current at approximately 1.6 volts. Reviewing our output choices I would select an open collector output to safety drive the current of the LED. I have now narrowed my choice of optical switches to the LLHP series.
8. The next step is to choose the correct models for the low and high alarm. To do this you must understand which operation you need to do and how to wire the output to have the LED turn on during the correct conditions. The LED circuit can be the same for both application but the switch operation will need to be different. An NPN open collector circuit would commonly drive the LED circuit. For the low alarm, I would choose a normally closed operation. This means the open collector output will be turned on when there isn’t any fluid on the optical switch. The low alarm would be a Model OPT4299-2. For the high alarm I would choose a normally open operation. This means the open collector will turn on when the fluid is present on the switch. The high alarm would be a Model OPT4299-1.
   

Designing the alarm circuit:

The drive circuit for either alarm LED would be as follows:

The value of the resistor would be calculated as follows:

R = (Supply voltage – LED Voltage – Open Collector Voltage Drop) / LED Drive Current
R = (24-1.6-0.3) / 0.020
R = 1,105 Ohms

Application Example #2:

Pump control is required for a small tank containing hot water. When the hot water reaches the low level a pump will turn on and stay on until the water level reaches the high level. There are M12 threaded fittings in the tank for an outside mounted switch located in both the high and low level location. The intent is to have a PLC do the pump up control logic. The PLC will be mounted in a panel near the tank. The PLC has digital inputs and is expecting the optical switch to provide a signal output “high” for the two positions. The water temperature ranges from 160ºF to 170ºF. The tank is not pressurized. There is 12 Vdc available for the power. The Optical Switch selection steps would be as follows:

9. Check to see if the Viscosity of the liquid to be measured is less then 2,000 cP. Water is 1 cP and will work very well with all our optical switches.
10. Check the housing material compatibility for use with water. All three materials will work.
11. Check the pressure requirement. The tank is not pressurized so all three materials will work.
12. Check the operating temperature. Not all models will operate within the 160ºF to 170ºF range.
13. Select the mounting type. The mounting is an outside mount with a M12 thread. The optical switch choice will now narrow to only those models available with the M12 thread for outside mount.
14. Choose the material of the optical switch. Due to the temperature range and M12 outside mount my choice would be the LLC series with a polysulfone housing.
15. Choose the correct input and output electrical specifications. The input power is available is 12 Vdc. The desired output is a digital signal with the output being high when the levels are reached. The both levels can be a direct digital output of the LLC series.
16. The next step is to choose the correct models for the low and high-level switches. For the low level, I would choose a digital output, high in air. This means the output will be turned on when there isn’t any fluid on the optical switch. The low level would be a Model OPT4306-3. For the high level, I would choose a digital output, low in air. The high alarm would be a Model OPT4306-5.

Wiring of the control circuit: