You cannot see a rod pump working a mile underground, so engineers read its health from a graph instead - the dynamometer card. This plot of load against position through a stroke is the single most powerful diagnostic for rod-lift wells. This guide explains what a dynamometer card is, the difference between surface and downhole cards, and what their shapes reveal.
Dynamometer Card in one line: A dynamometer card (dyna card) is a plot of load versus plunger position over one complete pumping stroke of a rod-lift well. A surface card plots polished-rod load against surface position; a downhole (pump) card is computed from it to represent load and position at the pump itself. The shape of the card is a signature that reveals how the pump and rod string are performing, making it the primary tool for diagnosing rod-pump problems.
A surface dynamometer card is measured directly: a load cell (or motor data) records polished-rod load while a position sensor tracks the rod's travel, producing a load-versus-position loop for each stroke. But the surface card is distorted by the elasticity and dynamics of the long sucker rod string - the rods stretch, rebound, and transmit vibrations, so the surface shape is not a clean picture of what the pump is doing.
The downhole, or pump, card solves this. Using a mathematical model of the rod string (a wave-equation solution), the surface data is transformed to compute the load and position at the pump depth, stripping out the rod dynamics. The result is a card that represents the pump's actual behavior, from which pump fillage, effective stroke, and valve action can be read directly. Modern pump-off controllers compute the downhole card automatically each stroke.
An ideal downhole card is close to a clean rectangle: load is picked up sharply as the traveling valve closes at the start of the upstroke, stays high across the upstroke as fluid is lifted, drops sharply as the traveling valve opens at the top, and stays low across the downstroke. Deviations from that rectangle are diagnostic. Rounded or shifted load pickup can mean a standing- or traveling-valve leak; a card that is narrow or shows load dropping late indicates low pump fillage.
Specific faults have specific shapes. Fluid pound shows the load collapsing partway down the upstroke where the plunger hits liquid after passing through gas or vapor. Gas interference and gas lock round off the card and shrink the effective stroke. Rod parting, tubing movement, a stuck plunger, and worn valves each leave recognizable signatures, which is why the dyna card is the diagnostic of choice for rod lift.
Dynamometer cards are generated at the well by a pump-off controller or dynamometer, which measures load and position and computes the surface and downhole cards continuously. Those cards, along with derived values like fillage, drive the controller's pump-off decisions and are stored for the operator to review.
A cloud SCADA such as Merobix reads the card data and pump metrics a controller exposes over Modbus or another supported protocol, so an operator can pull up dynamometer cards and fillage trends for wells across a field from a browser and spot a developing pump problem without a site visit. The controller computes the cards at the well; SCADA makes them - and the whole field's pump health - visible and comparable in one place.
It is a plot of load versus plunger position over one complete stroke of a rod-lift well. A surface card uses measured polished-rod load and surface position; a downhole card is computed from it to show the pump's own behavior. The card's shape is a diagnostic signature of how the pump and rod string are performing.
A surface card is measured directly at the polished rod but is distorted by the elastic dynamics of the long rod string. A downhole (pump) card is computed from the surface data using a rod-string model to represent load and position at the pump itself, giving a clean view of pump fillage and valve action.
The card shape reveals low pump fillage, fluid pound, gas interference and gas lock, standing- and traveling-valve leaks, a stuck or worn plunger, tubing movement, and a parted rod string. Each fault produces a recognizable deviation from the ideal card, making it the primary diagnostic for rod-lift wells.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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