TO: FAX: FOR: OMNIFLEX DATE: 25 February, 2016 PR No: PR11004IsolatorsIF (Rev 2) WORDS: 3265 TARGET: SEE LIST AT END STATUS: Approved NOTE:

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1 e8bbadecf0bd9a0fc9090ffile.doc (ev ) Press elease P.O. Box 79, Overport, 07 FAX: (0) 0808 TE: (0) ianl@omniflex.com TO: FAX: FO: OMNIFEX DATE: February, 0 P No: P00IsolatorsIF (ev ) WODS: TAGET: SEE IST AT END STATUS: Approved NOTE: P Material. How to fix your Plant Signal Interfaces Signal oop Problems trouble every plant every day The ubiquitous problem with every plant is the Interface of plant measurement signals to the monitoring and control systems. Unfortunately for many plants this is the single biggest area of weakness and with the success of the organization depending on these measurements more attention should be afforded to the integrity of signal conditioning systems. The problems faced by these systems are numerous: Aged Cabling and Interfaces ong Cable uns Earth oops Interference from other plant devices Floating Earth Potentials Isolation of signals from PC, SCADA and DCS egacy Instrumentation Isolate Grounded Equipment Adding Instruments to existing oops Poor Design Converting current loops into accurate V Protecting against open circuit loops oad dependency calibration The consequences are even more onerous on the bottom line e8bbadecf0bd9a0fc9090ffile.doc () of

2 Damaged PCs and DCS front end. Costs $$$ e8bbadecf0bd9a0fc9090ffile.doc (ev ) Downtime osses $$$ Inaccurate readings affect plant production oss $$$ Heavy eactive Plant Troubleshooting and Maintenance oad oss $$$ Many well informed Plant Owners and System Integrators fit signal conditioning interfaces as standard during the design phase the increase in cost on the signal interface more than pays for itself later in productivity and reliability. This is often sacrificed and traded off in the initial design. Omniflex has accumulated 0 years of experience in signal conditioning system design and has produced many innovative products in this particular field. etrofitting this to plant is easy with D rail mounted modules which can be located in marshalling panels or termination boxes. A compendium of common plant interface problems is addressed using oop Powered Isolators in the following article. oop Powered Isolators are a cost effective solution to solving loop problems Application : Using the PI to isolate a powered 0mA transmitter output from a resistive load P ow ered 0m A O utput 8 7 0m A 0m A P I 0m A This is the basic circuit for inserting a oop Powered Isolator (PI) into a current loop. The PI can simply be cut into any existing current loop to isolate the current transmitter from the load. NOTE: The side of the PI is always connected to the side of the loop supplying the loop power. The PI will consume less than Volts of the available loop voltage. This is equivalent to inserting less 0 ohms of additional resistance into the current loop. To determine the maximum loop resistance that you can tolerate in your cabling, apply the following formula: e8bbadecf0bd9a0fc9090ffile.doc () of

3 e8bbadecf0bd9a0fc9090ffile.doc (ev ) T 0 here: is the maximum resistance in the loop without causing measurement error. T is the maximum load resistance that the current transmitter can drive. is the total resistance of all loads in the loop (excluding the PI) A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). Application : Using the PI to isolate a field mounted 0mA twowire transmitter from a PC, TU or DCS oop P ow ered Tw ow ire Transm itter V 0m A 0m A P I 0m A 7 8 This is the basic circuit for isolating a fieldmounted twowire transmitter from the control circuitry using an PI. The PI can simply be cut into any existing twowire current loop to isolate the transmitter from the panel power supply. NOTE: The side of the PI is always connected to the side of the loop supplying the loop power, so in this application the twowire transmitter is connected to the OUT terminals of the PI. Because of the mm wire size capability of the PI terminals, the PI can also act as the field interface terminals, saving you the extra termination and wiring cost. For multiple loops where space is a concern, use the PD dual module. (See Application 7, 8 and 9) The PI will consume less than Volts of the available loop voltage. This is equivalent to inserting less 0 ohms of additional resistance into the current loop. e8bbadecf0bd9a0fc9090ffile.doc () of

4 e8bbadecf0bd9a0fc9090ffile.doc (ev ) To determine the maximum loop resistance that you can tolerate in your cabling, apply the following formula: ( VS min T min V.0 ) 0 is the maximum resistance in the loop without causing measurement error (in Ohms). V Smin is the minimum voltage of the power supply used to drive the loop (in Volts). V Tmin is the minimum voltage required by the twowire transmitter for operation (in Volts). is the total resistance of all loads in the loop (excluding the PI) (in Ohms) A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). Application : Using the PI s internal resistor with a wire transmitter to provide V to your PC/TU/DCS oop Pow ered Tw ow ire Transm itter 0m A P I V V V 7 8 There are many cases when using 0mA inputs to your PC or TU or DCS is inconvenient. For example:. Your analogue input does not support 0mA, and mounting an external resistor is inconvenient.. Your analogue input has plug in terminals, and you do not want to lose power to your field transmitter or disrupt the loop if the terminal block is unplugged. In these cases you can use the internal resistor on the side of the PI to conveniently convert your 0mA signal into a V signal. For the most accurate result, ensure that the reference of the PI (terminal 8), and the reference of your analogue input are referenced to the same point. NOTE: The side of the PI is always connected to the side of the loop supplying the loop power, so in this application the twowire transmitter is connected to the OUT terminals of the PI.Because of the mm wire size capability of the PI terminals, the PI can also act as the field interface terminals, saving you the extra termination and wiring cost. The PI will consume less than Volts of the available loop voltage. This is equivalent to inserting less 0 e8bbadecf0bd9a0fc9090ffile.doc () of

5 ohms of additional resistance into the current loop. e8bbadecf0bd9a0fc9090ffile.doc (ev ) To determine the maximum loop resistance that you can tolerate in your cabling in this application, apply the following formula: ( VS min T min V.0 ) 00 is the maximum resistance in the loop without causing measurement error (in Ohms). V Smin is the minimum voltage of the power supply used to drive the loop (in Volts). V Tmin is the minimum voltage required by the twowire transmitter for operation (in Volts). A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). Application : Using the PI s internal resistor with a wire transmitter to provide V to your PC/TU/DCS 8 7 V V 0m A P I There are many cases when using 0mA inputs to your PC or TU or DCS is inconvenient. For example:. Your analogue input does not support 0mA, and mounting an external resistor to convert the signal to V is inconvenient.. Your analogue input has plug in terminals, and you do not want to lose power to your field transmitter or disrupt the loop if the terminals are unplugged. In these cases you can use the internal resistor on the OUT side of the PI to conveniently convert your 0mA signal into a V signal. For the most accurate result, ensure that the reference to the PI (terminal ), and the reference of your analogue input are referenced to the same point. NOTE: The side of the PI is always connected to the side of the loop supplying the loop power, so in this application the fourwire transmitter is connected to the terminals of the PI. Because of the mm wire size capability of the PI terminals, the PI can also act as the field interface e8bbadecf0bd9a0fc9090ffile.doc () of

6 terminals, saving you the extra termination and wiring cost. e8bbadecf0bd9a0fc9090ffile.doc (ev ) The PI will consume less than 8 Volts of the available loop voltage. This is equivalent to inserting less than 00 ohms of resistance into the current loop. To determine the maximum loop resistance that you can tolerate in your cabling in this application, apply the following formula: T 00 is the maximum resistance in the loop without causing measurement error (in Ohms). T is the maximum load resistance that the current transmitter can drive (in Ohms). A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). Application : Using the PI s internal clamp with a wire transmitter to protect the loop against open circuit. oop P ow ered Tw ow ire Transm itter V 0m A 0m A P I 0m A 7 8 There are cases, when using 0mA inputs to your PC, TU or DCS, where it is important that the current loop is not disrupted when the analogue input to your PC or TU or DCS is unplugged or disconnected. In these cases you can use the internal clamp of the PI to protect the loop from open circuit if your PC or TU or DCS input is unplugged or disconnected. This is simply achieved by connecting the input clamp terminal to your reference. If the analogue input to your PC or TU or DCS is disconnected, the current will be diverted to through the clamp, saving the current loop from disconnection. The voltage across the PI will be clamped to.8volts in this condition only slightly higher than the normal operating voltage of Volts. This higher clamp voltage should be used when calculating maximum allowable loop resistance. NOTE: The side of the PI is always connected to the side of the loop supplying the loop power, so in this application the twowire transmitter is connected to the OUT terminals of the PI. e8bbadecf0bd9a0fc9090ffile.doc () of

7 e8bbadecf0bd9a0fc9090ffile.doc (ev ) Because of the mm wire size capability of the PI terminals, the PI can also act as the field interface terminals, saving you the extra termination and wiring cost. To determine the maximum loop resistance of your cabling that you can tolerate in your loop with the clamp in operation, apply the following formula: ( VS min T min V.0 ) 00 is the maximum resistance in the loop without causing measurement error (in Ohms). V Smin is the minimum voltage of the power supply used to drive the loop (in Volts). V Tmin is the minimum voltage required by the twowire transmitter for operation (in Volts). A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). Application : Using the PI s internal clamp with a wire transmitter to protect the loop against open circuit. e8bbadecf0bd9a0fc9090ffile.doc () 7 of

8 e8bbadecf0bd9a0fc9090ffile.doc (ev ) 8 7 0m A 0m A P I 0m A When using 0mA inputs to your PC, TU or DCS, there are cases where it is important that the current loop is not disrupted when the analogue input to your PC or TU or DCS is unplugged or disconnected. In these cases you can use the internal clamp of the PI to protect the loop from open circuit if your PC or TU or DCS input is unplugged or disconnected. In fourwire current transmitter applications this is simply achieved by connecting the output clamp terminal to the current output terminal of the PI. If the analogue input to your PC or TU or DCS is disconnected, the current will be diverted through the clamp, saving the current loop from disconnection. The voltage across the PI will be clamped to.8volts in this condition slightly higher than the normal operating voltage of Volts. This higher clamp voltage should be used when calculating maximum allowable loop resistance. NOTE: The side of the PI is always connected to the side of the loop supplying the loop power, so in this application the fourwire transmitter is connected to the terminals of the PI. Because of the mm wire size capability of the PI terminals, the PI can also act as the field interface terminals, saving you the extra termination and wiring cost. To determine the maximum loop resistance of your cabling that you can tolerate in your loop with the clamp in operation, apply the following formula: T 00 is the maximum resistance in the loop without causing measurement error (in Ohms). T is the maximum load resistance that the current transmitter can drive (in Ohms). A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). Application 7: Using the PD to isolate multiple 0mA Outputs from a PC or DCS e8bbadecf0bd9a0fc9090ffile.doc () 8 of

9 e8bbadecf0bd9a0fc9090ffile.doc (ev ) TU / P C / DCS 8 0m A 0m A 7 P D 0m A 0m A 0m A s 0m A input the load. In this application, the PD can be inserted directly into the 0mA output loops between the transmitter and Each PD circuit will consume less than Volts from the loop. For loop resistance calculation purposes this is equivalent to inserting an additional resistance of 0 ohms into the current loop. NOTE: The side of the PD is always connected to the side of the loop supplying the loop power, and so in this application, the Transmitter outputs are connected to the side of the PD. Because of the mm wire size capability of the PI terminals, the PI can also act as the field interface terminals, saving you the extra termination and wiring cost. To determine the maximum loop resistance of your cabling that you can tolerate in your loop, apply the following formula: T 0 is the maximum resistance in the loop without causing measurement error (in ohms). T is the maximum load resistance that the current transmitter can drive (in ohms). is the total resistance of all loads in the loop (excluding the PI) (in Ohms) A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). Application 8: Using the PD to isolate multiple 0mA inputs to a PC or TU (with passive inputs) e8bbadecf0bd9a0fc9090ffile.doc () 9 of

10 e8bbadecf0bd9a0fc9090ffile.doc (ev ) V dc 0m A 0m A 7 8 P D 0m A 0m A 0m A Passive inputs TU / P C In this application, the PD can be inserted directly into the 0mA input loops between the field mounted twowire transmitter and the PC or TU input. Each PD circuit will consume less than Volts from the loop. For loop resistance calculation purposes this is equivalent to inserting an additional resistance of 0 ohms into the current loop. NOTE: The side of the PD is always connected to the side of the loop supplying the loop power, and so in this application, the twowire transmitters are connected to the OUT side of the PD. Because of the mm wire size capability of the PD terminals, the PD can also act as the field interface terminals, saving you the extra termination and wiring cost. To determine the maximum loop resistance of your cabling that you can tolerate in your loop, apply the following formula: ( VS min T min V.0 ) 0 is the maximum resistance in the loop without causing measurement error (in Ohms). V Smin is the minimum voltage of the power supply used to drive the loop (in Volts). V Tmin is the minimum voltage required by the twowire transmitter for operation (in Volts). is the resistance of the PC/TU input (in Ohms) A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). Application 9: Using the PD to isolate multiple 0mA inputs to a DCS with active (twowire tx) inputs. e8bbadecf0bd9a0fc9090ffile.doc () 0 of

11 e8bbadecf0bd9a0fc9090ffile.doc (ev ) 0m A Twowire inputs ooppow ered Tw ow ire Transm itters 0m A 0m A 7 8 P D 0m A 0m A V DCS In this application, the PD can be inserted directly into the 0mA input loops between the field mounted twowire transmitter and the DCS input. Each PD circuit will consume less than Volts from the loop. For loop resistance calculation purposes this is equivalent to inserting an additional resistance of 0 ohms into the current loop. NOTE: The side of the PD is always connected to the side of the loop supplying the loop power, and so in this application, the twowire transmitters are connected to the OUT side of the PD. Because of the mm wire size capability of the PD terminals, the PD can also act as the field interface terminals, saving you the extra termination and wiring cost. To determine the maximum loop resistance of your cabling that you can tolerate in your loop, apply the following formula: ( VS min T min V.0 ) 0 is the maximum resistance in the loop without causing measurement error (in Ohms). V Smin is the minimum voltage of the power supply used to drive the loop (in Volts). V Tmin is the minimum voltage required by the twowire transmitter for operation (in Volts). is the resistance of the PC/TU input (in Ohms) A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). Application 0: Dealing with zero loop resistance when using the PI. e8bbadecf0bd9a0fc9090ffile.doc () of

12 e8bbadecf0bd9a0fc9090ffile.doc (ev ) P ow ered 0m A O utput 8 7 0m A 0m A P I 0m A < 00ohm s The PI is optimised to minimise the effective inserted loop impedance, but does require a minimum of 00 ohms of load impedance, (or volts) on the output to maintain operation. In some applications, when using fourwire transmitters, the load being driven is lower than this minimum value, and additional load needs to be inserted into the output loop to bring the minimum load up to the required 00 ohms. One solution for this is to use the internal 0 ohm resistor to provide this additional resistance. When connected as shown in the diagram above, the internal resistor is used in series with the current loop to provide an additional of loop resistance. This brings the PI back into specification without the need for any additional resistors. NOTE: The side of the PI is always connected to the side of the loop supplying the loop power, so in this application the fourwire transmitter is connected to the terminals of the PI. Because of the mm wire size capability of the PI terminals, the PI can also act as the field interface terminals, saving you the extra termination and wiring cost. To determine the maximum loop resistance of your cabling that you can tolerate in your loop with the clamp in operation, apply the following formula: T 00 is the maximum resistance in the loop without causing measurement error (in Ohms). T is the maximum load resistance that the current transmitter can drive (in Ohms). is the resistance of the connected load (in Ohms) A sensible value to use for this safety factor would be 00 ohms (equal to Volts at 0mA). e8bbadecf0bd9a0fc9090ffile.doc () of

13 Contact Ian oudon of OMNIflex on (0) 077 e8bbadecf0bd9a0fc9090ffile.doc (ev ) CHECKED BY (SIGNATUE) DATE e8bbadecf0bd9a0fc9090ffile.doc () of