This simple wall, or in some cases, flowmeter mounted instrument provides an analogue output proportional to flow. Three basic models are available offering 0/4 to 20 milliamp, 0 to 5 volt and 0 to 10 volt outputs. In all cases the offset and full scale adjustments are independent of each other.
Invinity to build 20MWh flow battery in UK
A surprising comment for someone who (I think you´ve said in the past) worked in the industry. National Grid have a variety of reserve service schemes...