The mass flow meter reading shows a negative value
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The first thing that comes to mind when a negative value is displayed is whether the installation direction is opposite to the flow direction of the medium; after verification, it was indeed the reverse. Then just set the flow direction of the medium in the flow meter. But what I want to ask is, 1. Can all mass flow meters measure in both directions? ? Also, before maintenance, if the flow meter shows a negative value, what value will be displayed on the DCS in the control room? Will there be a corresponding value as well? Will only one alarm value be displayed? When we checked it on the DCS, it showed a negative value that remained unchanged; but after setting the flow direction in the flow transmitter, it returned to normal! ...It’s not intelligent. If the flow direction is reversed, wouldn’t it be good if the signals sent to the DCS could still be displayed normally? Isn’t that right? Or am I wrong in thinking? 2. If measuring flow in a pipe with two-way flow, what type of flow meter is required?
Mass flow meters can all measure in both directions. To enable display on both sides of the DCS, set the range to -x.xx~+x.xx. If it is not set this way, it will either output an alarm value or a positive value.
I just want it to be able to output a value regardless of whether the flow is positive or negative; can’t it do that? Based on the problem I encountered, the DCS showed a negative set value at that time; it should have triggered an alarm. Couldn’t it at least give an alarm?
It depends on the specific functions of your watch – whether it has a two-way output feature.
Mass flow meters have a direction requirement and must not be installed in the reverse direction
Moreover, when installing, it is also necessary to consider whether the medium is in a liquid or gas phase; during use, if the medium is in liquid form, vaporization and other factors can cause pipeline vibration, leading to measurement errors
Mass flow meters can generally measure in both directions. For two-way measurement, porous orifice plates are usually used; wedge flow meters can also function in two directions. It should be possible to set the range between -max and +max. If two-way measurement is enabled, there should be no alerts, as the meter cannot determine whether a negative value indicates that the operating conditions have reversed or that there is a problem with the meter’s measurement. An alert will only occur if the meter is internally damaged. It’s necessary to ask the manufacturer about this, as design firms, when specifying requirements, only indicate that two-way measurement is possible or the normal positive and negative flow values, without providing specific instructions on how to configure the meter. . . .
The range is set such that the maximum value corresponds to a negative value and the minimum value to a positive value. Generally, flow meters are configured with a positive flow range; the on-site display can show negative flow values, but the signal sent to the DSC still corresponds to the positive range – otherwise, either an alarm is triggered or only positive values are displayed.
The method for two-way measurement with mass flow meters is exactly the same, but most manufacturers require it to be set by selecting “two-way” measurement during configuration.