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How to Program an 3100-series Rousemount Ultrasonic level transmitter.

Tue, 18 Jun 2013 07:44:30 +0100

First take the full range of level - say for example - 0 to 4mtr.
Now install the ULT above the level on some structural base. Clean the fase of sensor with soft tissue paper.
Now before Power up the transmitter checked that the inclination from sensor face to water is minimum...90 vertical preffred & there should not be any dust remain on sensor face. now power up the transmitter -say 24vdc, check across terminal.
before starting program see the water level is static or having riple on the surface.
now set B.erf - say 2.3 mtr (this is the distance from ensor face to water surface level) , set 4 ma = 0 , 20 ma = 20ma , & damping = 30sec in case of no ripple & 300 sec above in case of high ripple on surface of water.
After setting all this things you shall se the level in dcs as = 4mtr - 2.3mtr = 1.7 mtr (example)

after setting this check whether LE(echo lost) signal is comming on display or not , if not then your transmitter has been installed properly , if yes then please put the B.ref value properly.

incase of any doubt contact - pp.ic@rediffmail.com

How to detect earthy leakage field instruments (such as limit switches) connected to Field ...

Tue, 14 May 2013 12:00:37 +0100

Troubleshooting grounding problems can be difficult at best. It was not clear what you measured your voltage in reference to. In a floating DC system, if you read a voltage to ground, you have a ground in your circuit. If you do not, then your problem lies elsewhere (a problem with your system reference?). A cross connection to a different system can be a possible cause of this problem as can a bad power supply or a wiring mistake. Also, make sure that you do not have AC in your DC circuit

If you do have voltage to ground, you do have a ground in your power system but it is unlikely that a single ground would cause this problem (though not impossible) and a lot harder to find though there are ways to do it. When strange voltages appear in a system, it is commonly caused by a ground loop of some sort. One thing I would suggest is that you use the method Phil described at the closest you can get to your power supply upstream of any sensors and as much of your power distribution as you can and move outward toward your sensors to see if you can find ground loop current. This can eliminate the power distribution being involved and sometimes find the ground loop current path. Also note that the power supply does not necessarily have to be involved in the ground loop but can still be affected by it. If you still cannot find the ground loop, you can then try the sensors. Once you have found the first ground, you have done the easy part, finding the second ground can be more difficult and you should leave the first ground intact till you find the second ground. Also, be careful in disconnecting grounds as some times you do not know what they are connected to if there is another ground in the system.

It is also good to use your power system drawing or a system map to document as you go because these problems can be quite complex requiring some logic to figure out.

TROUBLESHOOTING CURRENT LOOPS

Fri, 12 Apr 2013 10:54:07 +0100

Troubleshooting Current Loops

A fundamental principle in instrumentation system troubleshooting is that every instrument has at least one input and at least one output, and that the output(s) should accurately correspond to the input(s). If an instrument’s output is not properly corresponding to its input according to the instrument’s design function, there must be something wrong with that instrument. Consider the inputs and outputs of several common instruments: transmitters, controllers, indicators, and control valves. Each of these instruments takes in (input) data in some form, and generates (output) data in some form. In any instrument “loop,” the output of one instrument feeds into the input of the next, such that information is passed from one instrument to another. By intercepting the data communicated between components of an instrument system, we are able to locate and isolate faults. In order to properly understand the intercepted data, we must understand the inputs and outputs of the respective instruments and the basic functions of those instruments. The following illustrations highlight inputs and outputs for instruments commonly found in control systems:

In order to check for proper correspondence between instrument inputs and outputs, we must be able to use appropriate test equipment to intercept the signals going into and out of those instruments. For 4-20 mA analog signal-based instruments, this means we must be able to use electrical meters capable of accurately measuring current and voltage.

Using a standard milliammeter to measure loop current

Since the signal of interest is represented by an electric current in an instrumentation current “loop” circuit, the obvious tool to use for troubleshooting is a multimeter capable of accurately measuring DC milliamperes. Unfortunately, though, there is a major disadvantage to the use of a milliammeter: the circuit must be “broken” at some point to connect the meter in series with the current, and this means the current will fall to 0 mA until the meter is connected (then fall to 0 mA when the meter is removed from the circuit). Interrupting the current means interrupting the flow of information conveyed by that current, be it a process measurement or a command signal to a final control element. This will have adverse effects on a control system unless certain preparatory steps are taken.

Before “breaking the loop” to connect your meter, one must first warn all appropriate personnel that the signal will be interrupted at least twice, falling to a value of -25% each time. If the signal to be interrupted is coming from a process transmitter to a controller, the controller should be placed in Manual mode so it will not cause an upset in the process (by moving the final control element in response to the sudden loss of PV signal). Also, process alarms should be temporarily disabled so they do not cause panic. If this current signal also drives process shutdown alarms, these should be temporarily disabled so that nothing shuts down upon interruption of the signal.

If the current signal to be interrupted is a command signal from a controller to a final control element, the final control element either needs to be manually overridden so as to hold a fixed setting while the signal varies, or it needs to be bypasses completely by some other device(s). If the final control element is a control valve, this typically takes the form of opening a bypass valve and closing at least one block valve:

Since the manually-operated bypass valve now performs the job that the automatic control valve used to, a human operator must remain posted at the bypass valve to carefully throttle it and maintain control of the process.

In consideration of the labor necessary to safely interrupt the current signal to a control valve in a live process, we see that the seemingly simple task of connecting a milli ammeter in series with a 4-20 mA current signal is not as easy as it may first appear.

MOTOR TESTING IN FIELD

Tue, 09 Apr 2013 10:57:38 +0100

When a motor overload or circuit breaker trips and /or blows fuses, certain procedures and tests should be carried out:

* lockout and tag out main circuit breaker;

* test insulation resistance of motor wires and windings by using megohm meter between T1, T2, & T3 leads and ground, then;

* test "T" leads to motor with ohmmeter for continuity and ohm-age of windings between A to B, B to C, A to C; each resistance should be within 1 or 2 ohms of each other; if the ohms readings are significantly different, or, if there is no continuity; go to the motor disconnect box, turn it off, perform the continuity and resistance test on the "T" leads, again; if the readings are good, the problem is in the wires from the motor controller to the disconnect switch;

* check the three wires by disconnecting all three wires from switch and twist together; go to controller and check for continuity between A to C, B to C, A to C; one or more wires will be open or grounded;

* correct solution is to pull all new wires in from controller to motor disconnect switch, whatever caused the problem may have damaged the other wires, also, replace all wires

* if problem is on motor side of disconnect switch, open motor connection box and disconnect motor;

* check motor for resistance to ground with megger, if reading is below 5mega ohms, motor is grounded and must be replaced;

* test motor windings for ohms between phases with ohmmeter A to B, B to C, A to C, readings should be within 1 or 2 ohms of each other; if readings indicate open or a significant ohm age difference, replace motor;

* if motor test readings are good, test the motor leads between the disconnect switch and the motor connection box for continuity and ground resistance, if readings are not good, replace wires;

* if all readings are OK, reconnect motor, remove lockout, and restore to service; the problem could have been mechanical in nature; an overload on motor caused by the chain, belt, bad bearings, faulty gearbox, or power glitch.
Motor Controller:

* check motor Full Load Current (FLC) at motor and check setting on controller overload (OL) device; most newer OL devices are adjustable between certain ranges, some older OL devices use heaters for a given amperage

* if circuit disconnecting means in controller is a circuit breaker, it should be sized correctly

* if the disconnecting means is a Motor Circuit Protector (MCP), the MCP must be correctly sized for the motor it is protecting and the MCP has a trip setting unit which has to be correctly set based on the Full Load Amperage of the motor; using a small screwdriver, push in on the screw head of the device and move to a multiple of thirteen of the FLC; example: a motor FLC of 10 amps would require that the MCP trip device be set to an instantaneous trip point of 130 amps
* fuses protecting the motor should be the dual element or current limiting type and based on the motor FLC

PROGRAMABLE LOGIC CONTROLLER

Thu, 11 Apr 2013 12:02:43 +0100

* check to ensure main power is on( 110 VAC)

* check 24V dc power available

* identify problem area

* check sensor operation in problem area

* check sensor Inputs to PLC

* check on PLC that a change in sensor state causes the corresponding Input LED on the PLC to go on or off

* identify Output controlled by Input on PLC ladder diagram

* ensure that Output LED is cycling on/off with Input

* check that Output voltage is correct and cycling on/off with Input

* locate Output device and ensure that voltage is reaching device and cycling with Input

* ensure that Output device is working correctly (solenoid coil, relay coil, contactor coil, etc.)

* an Input or Output module can be defective in one area or circuit and work correctly in all other circuits

* if each field circuit is not fuse protected, the modular internal circuit becomes a fuse and can be destroyed by a field short circuit or any other over-current condition

* check modular circuit; if bad, module must be replaced after correcting field fault

* shut down PLC prior to changing any module -main power and 24V power

* locate fault in field circuit by disconnecting wires at module and field device, check between wires for short circuit and to ground for short circuit; replace wire is short circuit found

* check device for ground, short circuit, mechanical and electrical operation, even when problem found in wires, always also check device for another fault, problem in wires can cause problem in device or vice versa; if device defective, replace device and then check total circuit before placing in operation and after restoring circuit, check again to ensure circuit and module are operating correctly

* check power supply module; if no output, shut down power and replace supply module

* back plane can go bad, some of the modules with power and others with no power, replace backplane

* sometimes, the PLC can be reset using the Reset key switch; ensure that turning the PLC off won't interrupt other running sub-set programs, turn keys witch to far right, after 15 seconds, turn to far left wait, then return to middle position; this operation should reset program and enable a restart

* the PLC program can have a latch relay with no reset under certain conditions, the key switch reset may have no affect on the latch, try turning the power to the PLC off and back on, this operation may reset the latch and allow the program to be restarted

* the PLC is usually part of a control circuit supplied with 110 VAC through a 440V/110V transformer as part of a system with motors, controllers, safety circuits, and other controls; occasionally, cycling the main 440V power off/on will be necessary to try to reset all the safety and control circuits

* possession and use of an up-to-date ladder diagram, elementary wiring diagram, manufacturer's manuals & diagrams, troubleshooting skills, operator's knowledge, and time are all required to solve issues involved in maintaining a modern manufacturing production line.