Detection of a blocked waterpump > alarm sign with histor

[elec_lover]

Hi, once the waterpump of the central heating system jammed ( blocked) :evil: . Single fase AC-Asynchronyous motor. No spinning components ar visible from outsite. If this happens: The motors current increments, te motor get hot en finally an internal thermal protection-switch
goes off. As the temperature of the motor windings decrements again, the protection switch closes again en everything starts over. But after a few error-cycles the motor could possible turn again. So I am not aware that a jam happended. I would like to a have alert to alert me that the pump was blocked. :idea: LED or whatever. So that I can decide to replace the pump. Any suggestion ? :roll:

 

[Dialtone]

You could do this in a couple of different ways.
1. Monitor the current draw on the motor to signal alarm if it rises above a pre-set value. Many commercial equipment monitoring systems use this technique to detect locked down motors and determine service times for wear related deterioration in performance.
2. Easiest would be to monitor the liquid flow in the system to set off an alarm. Look around at Hot Tub heaters. Most have a flow switch built into the heater tube that shuts the heating element down on low/no flow conditions. Could be easily modified to produce an alarm condition.
Dialtone

 

[Ali Sajjad]

U could also use a pressure switch that actuates the SPDT contacts on sensing high pressure in the flow line. The pressure setpoint of the pressure switch can be set at the shut-off pressure of the pump (mostly described in pump data sheets) or at some point above the normal discharge pressure of the pump.
Such pressure swtiches are easily available and and can be easily installed.

- Ali Sajjad

 

[elec_lover]

I prefer not to open the water circuit. But to measure the waterflow I could by measuring the temperature on the waterpipe and copare it with temp measured very close to the central water tank. "diff temp" and "voltage is supplied to pump" > it is not running.

 

[Klaus]

Measuring the temperature of water pipes has a considerable lag time.
Does the pump run continuously or does it cycle on and off? if it cycles then current measurements would be tricky as the starting up current is considerably bigger than the running current.
If you want instant blockade feedback you really need a water flow or pressure sensor since you cannot fit a motor shaft stall sensor.
If you wish to measure the temperature difference, how about measuring the motor case? It would get warmer when its stalled, while the thermal overload heats up. A monostable flip flop wired to an indicator should alert you that a blockade has occured.

 

[elec_lover]

Thank Y all for the responses.
If I measure the current (> voltage) it can be followed by an integrator. Higher current event must occur longer than n sec to alarm.
The water flow is cycled by a thermostate.
About measuring of the current: To avoid 230 Volt on the controller module, what shoult I use, optocoupler? tranformer coupling ?

 

[stevez]

While a common approach might be a flow switch to indicate flow or the lack of flow an approach that I might try - with a relay or two, temperature switch and a timer (or time delay relay) I'd sound an alarm if the thermostat was calling for heat - and after a short period of time the heat was not delivered. While this won't identify what is wrong it will call your attention to the call for heat and lack of proper response. That covers more possible failure modes including being bound up with air, clogging, pump locking up or failure of the burner. This might also be fairly easy to implement with a PIC or BASIC STAMP. "Aquastat" is one name for a thermostat that clamps on to a pipe to open/close with temp change.