Fluid Components International MT86, MT86HT Troubleshooting

CHAPTER 5 - TROUBLESHOOTING FLUID COMPONENTS INTL

5. Troubleshooting

Warning:

Caution:

Only qualified personnel should attempt to test this instrument. The operator assumes all
responsibilities for safe practices while troubleshooting.

The flow transmitter contains electrostatic discharge (ESD) sensitive devices. Use standard ESD
precautions when handling the flow transmitter. See Chapter 2, Installation, for ESD details.

Quick-Check Troubleshooting

At this point, observe the system setup to verify operation. Use Table 5-1 as a quick check of problems and
solutions. More in-depth discussions follow this table.

Table 5-1. Quick Check Troubleshooting

PROBLEM SOLUTION

No Output Check power application, check power supply fuse.
Flashing LED Set SW2 on the control board to the total number of sensing points.

Check all connectors for proper seating.
Switches SW1-1 through 1-3 should be open, 1-4 is a temp. comp. switch,
that is open when temp. comp. is used and closed when temp. comp. is not

Unexpected Outputs

used.
Check jumper positions (factory set positions are jumpers 1, 3, 5 and 7
installed).
The above switches and jumpers are on the control board.
Check the flow elements FLAT and FLOW ARROW versus the flow media.

Troubleshooting Equipment

2 each, Digital Multi-Meter (DMM) capable of measuring ohms, milliamps, and AC or DC voltage with a 4 1/2 digit

resolution.
3 each, precision decade resistance boxes (however they are optional if fixed precision resistors are used).
1 each, 1K ohm resistor for model MT86 or 100 ohms for model MT86HT.

Non-Maintenance Observations

At this point, observe the system setup to verify operation. No disassembly or testing is required at this time.

Check Serial Numbers

Verify that the serial number of the flow element(s) and the flow transmitter are the same. The flow elements and the
flow transmitter are a matched set and cannot be operated independently of each other. See Chapter 2 for a complete
explanation of serial numbers.

Check Input Power

Verify that the correct power source is turned on and connected.

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FLUID COMPONENTS INTL CHAPTER 5 - TROUBLESHOOTING

Check Instrument Installation

Review the instrument installation information given in Chapter 2 to verify correct mechanical and electrical
installation. Be sure the connectors are firmly mated, and the wires are firmly attached to the connector. (Be sure
the wires are inserted between the metal clamps and not between the clamp and plastic connector enclosure.)

Check for Moisture

Check for moisture in the enclosures. Moisture on the electronics can cause faulty operation.
If a component of the process media is near its saturation temperature, then the component may condense on the

sensing points. Liquid on the sensing points will drive the flow measurement higher than the true measurement.

Check Application Design Requirements

Application design problems usually occur with first time application instruments, although the design should also be
checked on instruments that have been in operation for some time. If the application design does not match field
conditions, errors occur.

1. Review the application design with plant operation personnel and plant engineers.

2. Ensure that plant equipment such as pressure and temperature instruments conform to the actual conditions.

3. Verify operating temperature, operating pressure, line size, and gas medium.

Check Flow Element Placement

If there are measurement errors check for process flow irregularities. A swirling or pulsating flow can exist near
valves, elbows and other obstructions. The flow element should be placed in a straight pipe run with 20 pipe
diameters upstream of the flow element, and 10 pipe diameters down stream of the flow element.

Check Flow Element Orientation

Verify that the FLAT on the flow element is parallel to the pipe and the FLOW ARROW points in the direction of
the flow stream. If the FLAT and the FLOW ARROW are not correct, the flow measurement will not be correct.
See Chapter 2 for the instructions on proper installation.

Check Proper Flow Element Insertion Depth

The flow element's sensing points must be located at the center line of the pipe unless the factory specifies otherwise.
Improper insertion depth may cause error in the flow measurement. See Chapter 2 for the instructions on proper
installation.

Check Flowmeter Switch Positions

Switches SW1-1, SW1-2 and SW1-3 should be in the open position. Switch SW1-4 should be in the open position if
the temperature compensation mode is used. Switch SW1-4 should be in the closed position if temperature
compensation is not being used. An easy way to verify temp. comp. is used is to see if the top of the null and gain
potentiometers have been sealed. If they are sealed the flowmeter is setup to use temperature compensation. If they
are not then no temperature compensation is used. (An open switch is the switch depressed on the left or lower side
of the switch bank.

Verify that the head-select switch SW2 is set on the number that corresponds to the last sensing point that is
connected to the flow transmitter.

Verify that the switch SW4 is in the OP position.

Troubleshooting Process

Verify Delta " R" Sheets

Verify that the Delta "R" sheets in the rear of this manual match the flowmeter's serial number. If there is a
miss-match the calibration could be incorrect. Contact FCI if the proper Delta "R" Sheets are missing.

Models MT86, MT86HT

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CHAPTER 5 - TROUBLESHOOTING FLUID COMPONENTS INTL

Verify Faulty Flow Elements

Caution:

Inform all personnel involved with monitoring the flow media that the flowmeter output readings
may change. The change of output could affect the plant peripheral equipment and or alarms.

To identify a bad flow element rotate the Head-Select switch, SW2, through its numbered positions. Pause at each
position to monitor a red Light Emitting Diode (LED), CR1. CR1 is located on the MT86 Control Board. If a
problem exists with a sensing point, the LED will flash. The LED may also flash if there is no sensing point that
corresponds to the switch position. If the Head-Select switch is pointing to a valid sensing point and the LED is
flashing the sensing point is bad.

Verify Resistance Readings

Use Figure 5-1 and Table 5-2 to determine if the flow elements are wired incorrectly or have failed. Turn the power
OFF to the flow transmitter. Unplug the problem flow element at the Input Board. Measure the resistances
described below by touching the DMM test leads to the terminal screws. (Remember to reconnect the flow element
when the troubleshooting is finished.)

Note:

If the system process does not allow the flowmeter power to be disconnected or the flow elements to be
unplugged then proceed to the section, In-Depth Troubleshooting - Voltage Measurements.

All resistances in Table 5-2 are based on a temperature of 32°F ( 0°C). Resistances across the ACT and the REF
RTDs for an MT86 are approximately 1000 ohms, resistances for an MT86HT are approximately 100 ohms. The
resistances will continue to increase for higher temperatures at the sensing points. Resistance values will vary with
temperature.

Table 5-2. Terminal Plug Resistances

Pin

Number

Approximate

Resistances

2 to 3 1000 Ohms*
2 to 4 1000 Ohms*
2 to 5 1000 Ohms*
2 to 6 1000 Ohms*
8 to 7 220 Ohms

*For the MT86HT flow element divide by 10.

Figure 5-1. Terminal Plug

The resistance of the active RTD will be greater than the resistance of the reference RTD whenever the heater is on
and the flow rate is below the high-limit flow. Also if the flowmeter has been on for some time, the resistance of the
active RTD will be greater than the reference until it cools down.

The flow element cable has a shield that ONLY connects to the flow transmitter side of the cable. There is no shield
connected to the flow element.

If one sensing point appears to be an open circuit and the other sensing point appears to be twice the resistance, a
wiring problem probably exists.

Voltage and current checks can be made on the flow elements. Before checking the flow element voltages and
current, other voltages need to be verified first. See the following paragraphs for the proper sequence of checks to
make.

If the flow element is bad, replace it with a spare flow element. Return the bad flow element to FCI for repair and, or
replacement. See Appendix C for the Customer Service return procedure.

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FLUID COMPONENTS INTL CHAPTER 5 - TROUBLESHOOTING

Troubleshooting Process - Voltage Measurements

Verify the use of the correct power source. Verify the power source is on and that the wiring matches the wiring
diagram in Figure 2-2 of Chapter 2.

If the flow element resistance and wiring check out, recheck the power supply; the fuse and the AC and DC voltages.
The power supply should be suspect when there seems to be multiple failures in the flowmeter.

Perform the following voltage checks with power applied to the flowmeter. The flowmeter should be put in normal
operating conditions. Make all measurements with the use of a DMM that has a differential (non-grounded) input.

Note:

The flow element sensing point voltage readings are for 1000 ohm RTDs.

Power Supply Source Voltages

Measure the power source at the power supply terminal block TS1 to be sure the correct power is applied.
Check the power supply voltages, using the test points provided. See Table 5-3 and Figure 5-2 for the proper operating

voltages. If the voltage checks are correct, the power supply is functioning properly.

Table 5-3. Power Supply Voltages - Power Supply Board

POSITIVE LEAD (+) NEGATIVE LEAD (-) MEASURED VALUE

TP1 TP4 28 Vdc ±1 Vdc
TP2 TP4 15 Vdc ±.6 Vdc
TP3 TP4 5 Vdc ±.3 Vdc
TP5 TP4 -5 Vdc ±.3 Vdc
TP6 TP4 -15 Vdc ±.6 Vdc
VC6 VGND -26.43 Vdc ±1 Vdc*
VC1 VGND 43.4 Vdc ±2 Vdc*

*Measurement points are not available on some power supplies.

If operating power is at terminal block TS1 and the test points do not have power, check fuse F1 on the power supply
board.

Remove power and unplug the power supply from the control board. Apply power to the power supply and re-measure
the voltages as shown in Table 5-4. If the voltage is still missing, then remove and replace the power supply.

Make the following measurements at the control board terminal strip. See Figure 5-3 and Table 5-4 for the
measurements.

Models MT86, MT86HT

Table 5-4. Power Supply Voltages - Control Board

Positive Lead (+) Negative Lead (-) Measured Value

TP15 TP16 10 Vdc ±.02 Vdc
RN1 PIN 3 TP16 5 Vdc ±.04 Vdc
U5 PIN 7 TP16 -10 Vdc ±.06 Vdc

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Figure 5-2. Electrical Assembly Layout

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