Metra Flow Meter – Instructions (6) Flow Alarm Outputs

Metraflow Meter – Flow Alarm Ouputs

aggressive fluid flow sensor
Single flow alarm:
Checking this option opens up input boxes for THRESHOLD; LATCHING and INVERT
Set the Threshold to the flow value you require the transistor to operate. The logic of operation can be adjusted with the INVERT check box (see left).
metraflow latching
The Latching box gives the user three options of None; High Threshold and Low Threshold.
  • “None” will cause the alarm to be triggered when the threshold flow is met. The alarm state will then reset in accordance with the user set Hysteresis.
  • “High Threshold” will cause an alarm signal to Latch on when flow is seen above the set value
  • “Low Threshold” will cause an alarm signal to Latch on when flow is seen below the set value
    Hysteresis (%): This is used when Latching is Set to NONE to prevent “fluttering” of the alarm signal when flow is around the threshold level.

LATCHED alarms will remain Active and the Local Display will show “LATCH” until they are reset. RESET LATCH ALARMS by either a signal Input on one of the other Input/Output PINS, or by Pressing and Holding the Left Hand Button on the Local Display on the Flow meter for 3 seconds.
Note the alarm points are driven by the display value on the “flow reading” screen. Any changes to the filter value of the display will affect the response time of the alarm points so there are two adjustable parameters to ensure “fluttering” does not happen with small flow fluctuations – response time and hysteresis.
INVERT – This Check box allows the user to invert the operation of the signal
• Checked – Alarm output logic HIGH
For details see the Alarm logic table or hover mouse over the set point to see the action of the output with the chosen settings.

metraflow dual flow alarm
Checking this will enable a range of flow to be entered. When the flow is outside/inside of this range the alarm will be triggered.
The remaining settings in the input box are the same as for Single Flow alarms.
  • When no Latching is chosen the alarm will automatically reset in proportion to the user set Hysteresis.
  • The Latched Alarm can be reset by a signal Input on one of the other Input/Output PINS, or by Pressing and Holding the Left Hand Button on the Local Display on the Flow meter for 3 seconds.
  • The INVERT checkbox will reverse the action of the alarm output. (see the Alarm Logic Table).
Metraflow – Reverse flow
metraflow ultrasonic reverse flow
This option allows the user to send a signal from the assigned wire/PIN when reverse flow is seen.
Selecting INVERT will reverse the action of the signal.
Metraflow PFA Flow Meter – Alarm Logic Display
metraflow alarm logic pure water and aggressive fluid flow meter
Alarm Logic Table for the Metraflow pure water and aggressive fluid flow meter
Metraflow Meter – Analogue Output
Metraflow Analogue Outputs
There are four options on the drop down menu: Not Used, 4-20mA, 0-5 Volt and 0-10 Volt.

When an analogue output is assigned the appropriate wire will then be activated:
• 4-20mA – Pink Wire
• 0-5Vdc – Red
• 0-10Vdc – Red
Once the selection has been made a further two boxes for entry of the analogue output at zero flow and full scale appear. These are numeric entries in the units and time base selected in calibration settings.

Metraflow meter outputs
It is possible to send a test signal at mA/V for each of the analogue output PIN/Wires.
Clicking T opens a menu where you can choose a % analogue output value which will be automatically sent for approximately 30 seconds.
Metraflow – Flow Details Tab

The large display reflects the meter readings showing on the Metraflow LCD Display. The RESULT DETAILS window below the large rate and total display shows the flow and total readings and the assignment of PIN6,7&8 whilst the meter is operational.

metraflow aggressive fluid flow meter
large display reflects the meter readings showing on the Metraflow LCD Display.
Metraflow Advanced User Tab

aggressive fluid flow sensors

Metrafow Interface Management

Protect (with PIN) Advanced Features Only: Allows users to restrict access to advanced pages.

Protect (with PIN) all controls: Allows users to restrict all configuration modifications to the system.

To use these features it is first necessary to create a PIN. This is a four digit number in the range 0001 to 9999. Setting a value of 0000 tells the software there is no PIN and this is how to remove the PIN. After allocating a PIN these check boxes can lock all of the settings or just the advanced user.

If you forget your PIN please contact you supplier for the default value. Once entered, all the setting parameters remain visible. In the ‘Help’ menu, the user can ‘Log On using PIN…’ but the user will be prompted for the PIN prior to making any changes. If the display version of the meter is being used and the display is set to view totals or rate and total the left hand button will cycle through the various options

Metraflow Meter Median filter

This filter removes short term anomalies in the recorded flow e.g. an air bubble passing through. It should be used with caution as it is theoretically possible that over use of this feature could lead to incorrect results in certain circumstances. Under normal operating conditions the meter returns around 25 results per second and a regular occurrence at this frequency could be completely ignored thus causing problematic readings.

The filter is a moving window taking the middle number from an odd number of results selectable between 1 and 21. It is not an average or mean and it is designed to totally ignore one or more results. A simple example is shown on page 18 for a median value of “3”.

recorded flow
Recorded flow used flow on the Metraflow Ultrasonic PFA flow sensors
Recorded and numerical order
Recorded and numerical order

The seventh flow in the table above is zero. This could have been a small bubble passing through the 240-020 meter which has a 1mm bore which could completely absorb the ultrasound. The median filter completely ignores this reading and for the zero reading returns the value of 3 from the results either side. This filter is particularly useful at low flows where a small dip in value could drop a result below the internal cut off levels.

Metraflow Meter Local Display

The Metraflow has local indication which is mimicked on the user interface software FLOW DETAILS tab and limited PUSH BUTTON interface ability.

  • The left hand button scrolls between TOTAL and RATE on the display. Press and Hold for 3 Seconds will RESET a LATCHED ALARM
  • Pressing the Right hand button will RESET the TOTAL FLOW Value.