Limit switches Mesa 5i25 and 7i76 combo

Hey folks;
I'm attempting to add limit switches in the form of Hall Effect Sensors to my new control system which consist of the subject components and DMM-Tech servos. The sensors are 3144 and I've used them for years on my old Mach 5volt system. For the new system, I've installed a 24Volt Field power supply to the new 7i76 card. The specs on the hall effects are 4.5 - 24 volt supply consuming a supply current of 4.4 mA.
The problem is, they are heating up to the point that they can't be touched. Way too hot. I've had one fail thus far so I disconnected the system.
Any ideas? I don't have any resisters in the line but I seem to remember reading that a resister is needed on the input to the card.
I do have the required resistor in the sensor (2200 ohm).
Any ideas?
Bill

As far as overheating goes, I dont know, 24V should be OK though its close the the devices limits. You might be better off with 12V field power if you want to use those sensors.

Pullup resistor are needed for NPN type sensors like the A3144, 2.2K should be OK

4.4 mA at 24 V should only dissipate 1/10th of a Watt, so no reason for them to heat up.
You might check the current on the supply terminal and see if it is close to 4.4 mA as per the spec. Do this with the sensor output disconnected to prevent further damage.

Then, depending on how the Mesa inputs are set up, the current limiting resistor there
may not be designed for a 24 V supply, so a series resistor may be needed.
I'm guessing this is where the heating is coming from. I might insert a 4.7 K Ohm resistor or thereabouts in series with the sensor output. Then, read the voltage across the resistor, and see if the sensor is being detected by the Mesa board.
If the Mesa board is using an opto-coupler input, it probably needs at least 4 mA to light the LED, that would get about 18 V for 4 mA through a 4.7K resistor.
Adjust resistor to get the correct current and reliable sensing on the Mesa inputs.

Jon

A 7I76 input resistance is 20K relative to I/O common (active high inputs) so needs a pullup to field power (12 or 24V) for NPN type sensors. PNP type sensors connect directly

Getting hot unfortunately suggests HALL device failure at 24V (or output shorted to + power)

Thanks for the info/advice guys. I replaced all the hall sensors with ss445 components made by honeywell. They appear to work much cooler than the Chinese components I was using so I'll give this a try. Still going to stay a 24 volts though.
Thanks Again.
Bill