Digital Positioner Boasts Flexibility, Performance

March 26, 2009
ABB’s Groundbreaking Features for Its New TZIDC Digital Positioner

Digital valve positioner product manager Naas DeJager showcased the new TZIDC digital valve positioner at a session called “Improve Flow Efficiency with Digital Valve Positioners,” but it could have been called “This Cool Positioner Does Everything You’ve Ever Asked For” instead.

For over an hour, DeJager reeled off product features along with how and where to use them. “This is an all-round positioner that we’ve designed to work with every kind of control valve,” DeJager said. “It can be configured to be a single- or double-acting actuator and can work as a linear actuator with plug and seat valves, or as a rotary actuator with ball and butterfly valves.”

DeJager noted that rotary valves have actuator-mounting standards from NAMUR and ISO, but that linear actuators are unstandardized. “We have designed mounting hardware that easily fits both rotary and linear requirements,” he said, “because we don’t make control valves, and we’re control-valve agnostic.”

The physical design of the TZIDC actuator is modular, allowing a remarkable range of options and features for customization. One of those features is the I/P (current-to-press) module, which is capable of withstanding vibration of up to 10 G at 80 Hz. “This design produces amazing stability even in high-vibration situations,” DeJager said. “It is much more stable than pilot or piezo implementations.”

“Nobody else can do any of this.” ABB’s Naas DeJager described the groundbreaking features of the company’s new TZIDC digital positioner.

In keeping with ABB’s emphasis on environmental payback, the TZIDC has the lowest steady-state air requirement of any valve positioner on the market: 0.015 scfm at steady state with a maximum of 6 scfm @ 90 psi. “Compare this to 0.8 scfm at steady state from the most commonly used positioner,” DeJager noted. “If you assume a cost of $0.01 per scfm and 50% steady state, this alone produces an annual environmental payback of over $2,000 per positioner. Multiply that by the hundreds of positioners in a typical refinery or chemical plant, and you can see how much the return can be.”

Rated SIL2 and offered in standard and hazardous area (Class I Div. 1) versions, the TZDIC is polyglot, speaking HART, WirelessHART with the forthcoming ABB WirelessHART adaptor, Profibus PA and Foundation fieldbus. Most of the functions of the positioner can be accomplished without a handheld communicator or PC-based software from the keypad on the device, and many keypad commands can be done without affecting operation of the positioner.

But wait, there’s more! This intelligent positioner has sophisticated control algorithms. It has slide-mode control to permit fast run-up to the setpoint without overshoot. It also has an advanced Autotune function that optimizes and minimizes positioner movement when the valve is on the setpoint. “It has an absolutely unique adaptive control algorithm not found in any other positioner on the market that permits field optimization of the positioner using the feedback module to overcome the effects of wear and tear, increased stiction and vibration and pulsation in the flow,” DeJager noted. “The only physical condition it can’t overcome is mechanical slop in the valve linkage. Nobody else can do any of this.”

And yet more! It easily sets up for split-range control with any range setting from 4 milliamps to 20 milliamps. It compensates for “dead angle.” “That’s the non-usable area of the characteristic curve, especially found in ball valves,” DeJager explained. “We can elevate the apparent zero so that the control system doesn’t think there’s excessive stiction in the valve travel and keep calling for more opening until it overshoots. The positioner also has a smart shutoff function, which is the inverse of dead angle.”

Combined with a huge range of diagnostics, the device management options for the TZIDC positioner are scaleable. DeJager said, “You can use the TZIDC with just a handheld HART communicator, or you can use it with laptop configurator software, or you can be continuously online with AssetVision Professional, either via a HART multiplexer, or using a WirelessHART network. This allows in-process data acquisition of four significant variables with time-stamped data that can be easily exported to spreadsheets like Microsoft Excel.”

Finally, it works with applications other than control valves. John Gregory, business development manager for actuators and positioners, noted, “There’s a huge installed base of old Bailey dampers out there, and we have a retrofit kit available using the TZIDC actuator to upgrade any damper that is still mechanically sound. This can provide huge energy savings to our existing damper users,” he said, “with payback times in three or four months or better in some cases.”