# Thread: Problem With IH Limit Switch.

1. ## Problem With IH Limit Switch.

I wonder if you guys can help me. I have a set of IH Limit Switches that I am going to be installing on a CNC Milling Machine. There seems to be a discrepancy with the outputs of one of these units. When powered with 5 volts the output of the white wire is approximately 1 volt less than the output of the green wire. See results below:

Limit Switch A
Green wire output = 4.85 volts.
White wire output = 3.98 volts.

Limit Switch B
Green wire output = 4.85 volts.
White wire output = 4.85 volts.

Obviously there is something wrong with the circuit for the white output wire of Limit Switch A. I am thinking that it has either had the wrong value of resister installed or possibly has a defective Optical Sensor. Has anyone noticed this before? Being as these Sensors are Epoxy into the housing it is next to impossible to remove them without damage. Does anyone know what the part number is for these Optical Sensors? If I knew the PN I could remove the old Sensor/PCB, repair the circuit and re-install everything with new Optical Sensors.

I have sent multiple Emails to Arron with no response on this matter. Any help would be appreciated.

Willyb

2. There doesn't appear to be any problem with the switches.
The variation in voltage is normal, logic devices don't need to be identical or have matched outputs.

TTL Logic Family
The transistor-transistor-logic (TTL) family was developed in the use of transistor switches for logical operations and defines the binary values as

0 V to 0.8 V = logic 0
2 V to 5 V = logic 1

3. Question,
What exactly is an "IH Limit Switch", there is nothing in Google reflecting that phrase!
Eric

4. I will rely on Mike's response for the logic part.

Regarding the removal of the PCB. It will snap out just fine. The epoxy grip is not that strong where it would damage the PCB. I had optical limits based on 5V circuitry. I needed 12 volt ones. Aaron sent me the replacements. I just took a screw driver, snapped the old ones out (gently) and epoxied in the new ones.

But hopefully nothing is wrong with yours and you will not have to do this.

Chris

• Originally Posted by widgitmaster
Question,
What exactly is an "IH Limit Switch", there is nothing in Google reflecting that phrase!
Eric

It's the limit switch built by Industrial Hobbies...

• Thank you dammachines !

Eric