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Recent content by roydm

  1. roydm

    Steam Purge of Pressure Impulse Lines

    Looking at my steam tables it's obviously superheated steam. I would just treat it as a normal blow-down, drop off the line and go down a few feet then tee off and slope back up into the transmitter with a blow-down valve at the bottom. When you blow it down the vertical pipe is going to grow...
  2. roydm

    Modbus RS-485 question

    As Gunnar says "Given that RS 485 is nothing but a differential mode classic RS 232 link " I have often used a laptop with serial port in terminal mode to monitor communications. I just forget how I connect it exactly but one of the RS-485 wires makes no sense at all, the other works well...
  3. roydm

    Limiting PID Output

    Anti Reset Windup is another term used, as Curt says a standard feature of most controllers to be implemented by an interlock action, it could clamp the output at any point. Not the same as an output limit which would fix it at some max or min value.
  4. roydm

    Level Transmitters vs. Leve Gauge Readings

    It could well be due to the different principle of measurement. The level gauge is probably using a float which will be partially immersed whereas the transmitter could be bouncing a signal off the surface. If you could let us know the make and model no we could make a more accurate guess.
  5. roydm

    Impedance Heating Power Control

    Lionel, Yes BC We are currently looking at 3500 Amps at 48 VAC for the secondary windings, a single phase transformer per phase. I'm trying to get my head around the size and form of the conductors in the winding.
  6. roydm

    What is the difference between an anti-static mat and a rubber insulating mat?

    I remember having to test the operating room floor but not how we did it, I assume it was a Megger we used
  7. roydm

    what is the type of light in power cord plugs that indicate power is on?

    Keith, I never knew that, I often wondered why they faded.
  8. roydm

    Impedance Heating Power Control

    Thank-you Gentlemen, that's the sort of input I was hoping for. An experimental system we built years ago used phase angle control with a period of seconds rather than minutes. I believe we used standard off the shelf 24 Volt transformers of about 5 KVA each but it sounds like we should be...
  9. roydm

    Impedance Heating Power Control

    I'm fairly familiar with using Zero crossover SCR controls for large resistive heating loads but what is the best method of controlling a transformer supplied heat load, I seem to recall that the transformer should be phase angle controlled. I am looking at 400 - 500 KW load. Thanks in advance.
  10. roydm

    Can a Foreign Degree Holder with Int'l Experience in Trade Job become a Journeyman In Canada?

    I am an overseas electrician now living in Canada, All I had to do was sit the trades examination, actually if I recall correctly it was just the Code section. Another avenue might be to seek employment with a factory maintenance company maintaining electrical equipment but not having to know...
  11. roydm

    self actuated pressure regulators

    You call it a self acting regulator, I interpret that as a simple spring and diaphragm, this type of regulator has significant droop (pressure loss with flow) You want to increase the flow by 37% I expect that would cause a significant drop in pressure, only the designer of vendor can tell you...
  12. roydm

    Pros and cons of single phase valve actuators

    I would think it depends on the size and speed requirement. If high speed is a requirement it's pretty hard to beat an air powered actuator. Large dampers often have electric actuators. Small single phase actuators incorporating a capacitor to get the phase shift are quite reliable and can be...
  13. roydm

    Pressure Trasnsmiter*

    You need to post a simple Process and Instrument Diagram showing where the transmitter is located and what it is doing. From your description it's in the pump suction, it's hard to imagine why you would need a 500 psi transmitter there. If the transmitter is connected to pump discharge will...
  14. roydm

    Recommendations for actuating a 30 kW heater

    Keith is absolutely right, you need all sorts of direct acting safety devices. By direct acting I mean not reliant on PLC, DCS or instrument power supply. One that I remember was a lube oil heater controlled by the PLC with an RTD inside the tank. Someone turned off the instrument power supply...
  15. roydm

    Recommendations for actuating a 30 kW heater

    Usually electric heating is controlled via a solid state time proportional power controller. This cycles the power On/Off over the period of a few seconds depending on the output from a temperature controller delivering complete half cycles. (the tyristors are switched on as Voltage passes...
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