Issue:
How many sensors can be powered by an MP503, MP580
Resolution:
24 VDC Supply
All three of the following components will supply 24 VDC to run sensors and transducers. The 24 VDC output of each is under microprocessor control. If the current draw is greater than the design maximum, the microprocessor will turn the output off (this is called a crowbar circuit). The current draw is then tested periodically, typically 1 attempt/second. If the current draw is still greater than maximum, the output will be turned off again. If the current draw is less than maximum, the output will stay on.
Many transmitters and sensors draw far more current when starting then when running. Vendor cut sheets all show the running current draw. Tests have shown that a 30 mA device will often draw 450 mA when starting.
While there is some temperature sensitivity affecting the crowbar circuit described, the effects are negligible below 50 C. The MP580, EX-2 and MP503 24 VDC supply circuits have been updated such that they will allow the maximum current draw up to 70 C.
MP580 24 VDC output will turn off if current draw greater than 250 mA (green board) or 650 mA (blue board). See also Blue MP580/581 24 Vdc power supply for problems with Rev E, F, and G blue boards.
EX2 24 VDC output will turn off if current draw greater than 200 mA.
MP503 24 VDC output will turn off if current draw greater than 120 mA.
Workaround
Install a Kele CLM-20 in series with 24 vdc power input of each sensor. The CLM will limit current to 20ma to the sensor module power. For example. the MP503 could power 4 humidity sensors rated for 25 ma at 24 vdc. The 24 volt power supply on the MP503 is rated for 120 ma. The MP503 processor will not drop 24 vdc power because of a high inrush current
You could also use a separate power supply for the sensors.
Notes:
Changes:
Other Question/Problem/Cause Statements:
- MP503 temperature and humidity sensor do not work at the same time
- this device will not power all the sensors
- What limits the number of sensors that can be powered off the internal power supply
- power supply limits
- MP503 - 4-20 mA humidity sensors on 24 Vdc power failure
- Can use same DC power supply to power up two Humidity sensors,
- current inputs on MP503
Facts:
- TRACER MP503
- Tracer MP580/581