Remotely configurable analog/digital input circuit and related apparatus and method

An apparatus includes first and second input terminals configured to be coupled to one of multiple types of input sources. The apparatus also includes a diode and a resistor coupled in series between the first and second input terminals. The apparatus further includes a plurality of switches each coupled to at least one of the diode and the resistor. The switches are configured to be opened and closed to reconfigure the apparatus depending on the type of input source. The switches could include a first switch coupled to the first input terminal, a current source, and a first side of the diode. The switches could also include a second switch coupled to the current source, a second side of the diode, and a first side of the resistor. In addition, the switches could include a third switch coupled to the second input terminal and a second side of the resistor.

TECHNICAL FIELD

This disclosure relates generally to process control and monitoring systems and other systems. More specifically, this disclosure relates to a remotely configurable analog/digital input circuit and related apparatus and method.

BACKGROUND

A process monitoring and control system may include wireless sensors used to measure various characteristics within an industrial facility. Physical transducers coupled to or used in the wireless sensors may have any of several types of electrical characteristics, such as high-level analog inputs (HLAIs), low-level analog inputs (LLAIs), and digital (ON/OFF) contact-closure inputs. Example HLAI signal sources include 0-20 mA or 4-20 mA current sources. Example LLAI signal sources include thermocouples and other sensors with outputs ranging from ±0.01V to ±0.1V.

In conventional systems, it is typically necessary to add a current shunt resistor across input terminals of a wired or wireless sensor in order to change an input of the sensor from accepting a low-level (voltage) input to accepting a high-level (current) input. Adding or removing the current shunt resistor requires access to field wiring terminals in order to manually add or remove the resistor from the sensor. An alternate approach uses an electromechanical switch to break the circuit to the shunt resistor, but this approach still requires physical access to the sensor in order to operate the switch manually.

Physical access to a sensor may be difficult or dangerous. For example, the sensor may be located in a hazardous environment or a difficult-to-access location, such as at the top of a tower. Also, for protection from moisture or corrosive environments, electronic components in a sensor may be conformally coated, making it impractical to use a removable resistor or an electromechanical switch.

SUMMARY

This disclosure provides a remotely configurable analog/digital input circuit and related apparatus and method.

In a first embodiment, an apparatus includes first and second input terminals configured to be coupled to one of multiple types of input sources. The apparatus also includes a diode and a resistor coupled in series between the first and second input terminals. The apparatus further includes a plurality of switches each coupled to at least one of the diode and the resistor. The switches are configured to be opened and closed to reconfigure the apparatus depending on the type of input source.

In a second embodiment, a system includes an input circuit configured to be coupled to one of multiple types of input sources. The system also includes circuitry configured to receive an input signal from the input source through the input circuit and to process the input signal. The input circuit includes a plurality of switches configured to be remotely opened and closed to reconfigure the input circuit depending on the type of input source coupled to the input circuit.

In a third embodiment, a method includes coupling an input source to an input circuit. The method also includes remotely adjusting a configuration of the input circuit based on a type of the input source, where the input source includes one of multiple types of input sources. The method further includes providing via the input circuit an input signal from the input source to circuitry for processing the input signal.

DETAILED DESCRIPTION

FIG. 1illustrates an example process control system100according to this disclosure. The embodiment of the process control system100shown inFIG. 1is for illustration only. Other embodiments of the process control system100could be used without departing from the scope of this disclosure.

In this example embodiment, the process control system100includes one or more process elements102. The process elements102represent components in a process system that perform any of a wide variety of functions. For example, the process elements102could represent sensors, actuators, or any other or additional industrial equipment in a processing environment. Each process element102includes any suitable structure for performing one or more functions in a process system. Also, a process system may represent any system or portion thereof configured to process one or more materials in some manner.

A controller104is coupled to the process elements102. The controller104controls the operation of one or more of the process elements102. For example, the controller104could receive information associated with the process system, such as sensor measurements from some of the process elements102. The controller104could use this information to provide control signals to others of the process elements102, thereby adjusting the operation of those process elements102. The controller104includes any hardware, software, firmware, or combination thereof for controlling one or more process elements102. The controller104could, for example, represent a computing device executing a MICROSOFT WINDOWS operating system.

A network106facilitates communication between various components in the system100. For example, the network106may communicate Internet Protocol (IP) packets, frame relay frames, Asynchronous Transfer Mode (ATM) cells, or other suitable information between network addresses. The network106may include one or more local area networks, metropolitan area networks, wide area networks (WANs), all or a portion of a global network, or any other communication system or systems at one or more locations. In some embodiments, the network106could represent multiple networks, such as a pair of Ethernet networks or a FAULT TOLERANT ETHERNET (FTE) network from HONEYWELL INTERNATIONAL INC. (which includes a redundant pair of Ethernet networks).

InFIG. 1, the process control system100also includes one or more wireless networks for communicating with wireless sensors or other devices. In this example, a wireless network includes infrastructure nodes (“I nodes”)108a-108e, leaf nodes110a-110e, and a gateway infrastructure node112.

The infrastructure nodes108a-108eand the leaf nodes110a-110eengage in wireless communications with each other. For example, the infrastructure nodes108a-108emay receive data transmitted over the network106(via the gateway infrastructure node112) and wirelessly communicate the data to the leaf nodes110a-110e. Similarly, the leaf nodes110a-110emay wirelessly communicate data to the infrastructure nodes108a-108efor forwarding to the network106(via the gateway infrastructure node112). In addition, the infrastructure nodes108a-108emay wirelessly exchange data with one another. In this way, the infrastructure nodes form a wireless network capable of providing wireless coverage to leaf nodes and other devices in a specified area, such as a large industrial complex.

In this example, the nodes108a-108eand110a-110eare divided into infrastructure nodes and leaf nodes. The infrastructure nodes108a-108etypically represent routing devices that can store and forward messages for other devices. Infrastructure nodes108a-108eare typically line-powered devices, meaning these nodes receive operating power from an external source. Infrastructure nodes108a-108eare typically not limited in their operations since they need not minimize power consumption to increase the operational life of their internal power supplies. On the other hand, leaf nodes110a-110etypically represent devices powered by local power supplies, such as nodes that receive operating power from internal batteries or other internal power supplies. Leaf nodes110a-110eare often more limited in their operations in order to help preserve the operational life of their internal power supplies. The leaf nodes110a-110emay represent routing or non-routing devices.

The nodes108a-108eand110a-110ecould also include other functionality, such as functionality for generating or using data communicated over the wireless network. For example, the leaf nodes110a-110ecould represent wireless sensors used to measure various characteristics within an industrial facility. The sensors could collect and communicate sensor readings to the controller104via the gateway typically represented by node112. The leaf nodes110a-110ecould also represent actuators that receive control signals from the controller104and adjust the operation of the industrial facility. In this way, the leaf nodes may include or operate in a similar manner as the process elements102physically connected to the controller104. The leaf nodes110a-110ecould further represent handheld user devices (such as INTELATRAC devices from HONEYWELL INTERNATIONAL INC.), mobile stations, programmable logic controllers, or any other or additional devices. The infrastructure nodes108a-108emay also include any of the functionality of the leaf nodes110a-110eor the controller104.

The gateway infrastructure node112communicates wirelessly with, transmits data to, and receives data from one or more infrastructure nodes and possibly one or more leaf nodes. The gateway infrastructure node112may convert data between protocol(s) used by the network106and protocol(s) used by the nodes108a-108eand110a-110e. For example, the gateway infrastructure node112could convert Ethernet-formatted data transported over the network106into a wireless protocol format (such as an IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.15.3, 802.15.4, or 802.16 format) used by the nodes108a-108eand110a-110e. The gateway infrastructure node112could also convert data received from one or more of the nodes108a-108eand110a-110einto Ethernet-formatted data for transmission over the network106. In addition, the gateway infrastructure node112could support various functions, such as network creation and security, used to create and maintain a wireless network. The gateway infrastructure node112includes any suitable structure for facilitating communication between components or networks using different protocols.

In particular embodiments, the various nodes in the wireless network ofFIG. 1form a mesh network communicating at 2.4 GHz or 5.8 GHz. A particular example of a wireless mesh network is the ONEWIRELESS network from HONEYWELL INTERNATIONAL INC. Also, in particular embodiments, data can be injected into the wireless mesh network through the infrastructure nodes or leaf nodes, thus providing versatile, multifunctional, plant-wide coverage for wireless sensing, asset location tracking, personnel tracking, wireless communications, and any other or additional functionality as desired.

A wireless configuration and Object Linking and Embedding (OLE) for Process Control (OPC) server114can configure and control various aspects of the process control system100. For example, the server114could configure the operation of the nodes108a-108e,110a-110e, and112. The server114could also support security in the process control system100, such as by distributing cryptographic keys or other security data to various components in the process control system100(like the nodes108a-108e,110a-110e, and112). The server114includes any hardware, software, firmware, or combination thereof for configuring wireless networks and providing security information.

A control room116in the process control system100typically represents a room or other area containing operator stations (such as desktop computers or computer terminals) used by human operators. The operator stations in the control room116typically receive data associated with operation of the process control system. The operator stations in the control room116also typically include various displays presenting that information to human operators. The operator stations in the control room116further typically allow the operators to review current and historical data associated with the operation of the process control system and to adjust the operation of the process control system. As a particular example, the operator stations often allow the operators to make manual adjustments to controllers104or to otherwise control the operation of the process control system from the control room116.

As described in more detail below, various components of the system100(such as process elements102and leaf nodes110a-110e) include one or more remotely configurable analog/digital input circuits. These circuits can be remotely configured, such as from the control room116or from portable user devices. As particular examples, each of these circuits can be remotely configured to represent a high-level analog input (HLAI), a low-level analog input (LLAI), or a digital input (DI) such as a contact-closure input. For instance, each reconfigurable circuit could include a semiconductor diode connected in series with a current shunt resistor across an input. A plurality of switches couple an analog-to-digital converter (ADC) or other circuitry to the diode and the current shunt resistor in a selectable circuit configuration. The ADC or other circuitry is operable to measure or otherwise use a state of a current source, voltage source, or switch closure coupled to the input. In this way, the remotely configurable input circuit can be reconfigured as needed without opening the device containing the input circuit. In fact, the device containing the input circuit need not be physically accessed by any personnel in order to perform the reconfiguration.

AlthoughFIG. 1illustrates one example of a process control system100, various changes may be made toFIG. 1. For example, the process control system100could include any number of process elements, controllers, networks (wired or wireless), infrastructure nodes (gateway or other), leaf nodes, servers, and control rooms. Also, the functional division shown inFIG. 1is for illustration only. Various components inFIG. 1could be combined, subdivided, or omitted and additional components could be added according to particular needs. In addition,FIG. 1illustrates one example of an operational environment where remotely configurable analog/digital input circuits could be used. These input circuits could be used in any other suitable device or system (whether or not related to process control).

FIG. 2illustrates an example device200having at least one remotely configurable analog/digital input circuit according to this disclosure. The device200could, for example, form part of a process element102or leaf node110a-110einFIG. 1or other device having a reconfigurable input.

As shown inFIG. 2, the device200includes an analog-to-digital converter202or other circuit. The analog-to-digital converter202generates a digital output corresponding to an analog input received at its two inputs INPUT±. While shown as including an analog-to-digital converter202, any suitable circuitry could be used in place of the analog-to-digital converter202.

The device200also includes two reconfigurable inputs204-206. Each reconfigurable input204-206includes two input terminals208a-208b, which can be coupled to different input sources. In this example, the input sources include a digital source210, an HLAI source212, and an LLAI source214. Each of the terminals208a-208bincludes any suitable structure for coupling to an input source.

Each reconfigurable input204-206also includes a semiconductor diode216connected in series with a current shunt resistor218across the input terminals208a-208b. The semiconductor diode216includes any suitable structure for supporting current flow in substantially one direction. The current shunt resistor218includes any suitable resistor having any suitable resistance.

Three semiconductor switches220-224are coupled to the semiconductor diode216and the current shunt resistor218. In particular, the semiconductor switch220is coupled to one end of the diode216, the semiconductor switch222is coupled to the other end of the diode216and one end of the resistor218, and the semiconductor switch224is coupled to the other end of the resistor224. The semiconductor switches220-224can be opened and closed to reconfigure the electrical connections involving the diode216, the resistor218, and the analog-to-digital converter202. In this way, the reconfigurable input204-206can be configured appropriately to handle a specified type of input. Each of the semiconductor switches220-224includes any suitable switching device, such as a field effect transistor (FET) or an optically coupled MOSFET or “photo-relay” device.

A current source226is coupled to the semiconductor switches220-222. The current source226generates a current used to detect whether a digital input is opened or closed. The current source226includes any suitable structure for generating a current, such as a MOS current source.

A controller228controls the operation of the device200, such as by setting or adjusting a configuration of the device200. For example, the controller228could receive data from an external source (such as over a wired or wireless connection) identifying a desired configuration of one or more input circuits204-206. The controller228could then open and/or close the switches220-224to configure the one or more input circuits appropriately. In this way, the device200can be remotely configured by providing suitable data to the controller228and the controller228providing suitable control signals to the switches. The controller228includes any suitable structure for controlling the configuration of at least one input circuit, such as a microprocessor, microcontroller, field programmable gate array, application specific integrated circuit, or other processing or control device.

FIGS. 3-5illustrate example configurations of the remotely configurable analog/digital input circuit204-206according to this disclosure. As shown inFIG. 3, when an HLAI current source212is being used, the HLAI source212may be connected to input terminals208a-208bof the device200such that the diode216is forward biased. Doing so allows current from the HLAI source212to flow though the current shunt resistor218. The voltage across the resistor218is measured by energizing the transistors222-224to connect the voltage signal to the analog-to-digital converter202, and the transistor220is opened.

As shown inFIG. 4, when an LLAI source214such as a thermocouple is being used, the LLAI source214may be connected to the input terminals208a-208bin the opposite polarity compared to the HLAI source212. In this case, the diode216blocks current from flowing through the resistor218. The LLAI source's input may be measured by energizing the transistors220and224to connect the input signal to the analog-to-digital converter202, and the transistor222is opened.

As shown inFIG. 5, when a digital source210is being used, the digital source210may be measured by connecting the current source226to the input terminals208a-208busing a polarity that is blocked by the diode216. The digital input may be measured by energizing the transistors220and224to connect the input signal to the analog-to-digital converter202in order to measure a voltage drop across the input contacts208a-208b.

The device200ofFIG. 2provides for the remote configuration of the reconfigurable inputs204-206. The device200can therefore eliminate the need for physical access to the terminals208a-208bor to any part of the device200. The device200here can accommodate multiple types of inputs (such as HLAI, LLAI, and digital inputs) without requiring the manual addition or removal of a current shunt resistor and without requiring manual operation of a switch. All components of the device200may be conformally coated for protection from moisture or corrosive environments. The device200may be mounted in a hazardous environment and be configured without opening the device.

AlthoughFIG. 2illustrates an example device200having at least one remotely configurable analog/digital input circuit, various changes may be made toFIG. 2. For example, the device200could include any number of reconfigurable inputs, such as a single input or more than two inputs. Also, any other or additional types of input sources could be coupled to a reconfigurable input. AlthoughFIGS. 3-5illustrate example configurations of a remotely configurable analog/digital input circuit204-206, various changes may be made toFIGS. 3-5. For instance, any other or additional types of input sources requiring similar or different configurations of an input circuit could be used.

FIG. 6illustrates another example device600having at least one remotely configurable analog/digital input circuit according to this disclosure. The device600could, for example, form part of a process element102or leaf node110a-110einFIG. 1or other device having a reconfigurable input.

As shown inFIG. 6, the device600includes an analog-to-digital converter602or other circuit that can receive and process three or more inputs AIN1-AIN3. The device600also includes three inputs604-608, at least two of which are configurable. The first input604includes two input terminals610a-610bwith a semiconductor diode612and a current shunt resistor614coupled in series between the terminals610a-610b. Another resistor616is coupled in parallel with the diode612. One transistor618is coupled to first ends of the diode612and resistor616. Another transistor620is coupled to second ends of the diode612and resistor616and to a first end of the resistor614. A third transistor622is coupled to a second end of the resistor614.

The second input606includes two input terminals624a-624bwith a semiconductor diode626and a current shunt resistor628coupled in series between the terminals624a-624b. One transistor630is coupled to a first end of the diode626. Another transistor632is coupled to a second end of the diode626and to a first end of the resistor628. A third transistor634is coupled to a second end of the resistor628.

The third input608includes two input terminals636a-636bwith a resistor638coupled between the terminals636a-636b. A resistor640is coupled to the resistor638, and a resistor642is coupled to the resistor640. One transistor644is coupled to first ends of the resistors638-640. Another transistor646is coupled to second ends of the resistors638-640and to the resistor642.

A current source648may be used within or external to the analog-to-digital converter602to generate a current used for sensing a status of at least one digital input. Four diodes650are placed across a first pair of inputs AIN1of the analog-to-digital converter602. These diodes650include multiple diode pairs (connected as a redundant pair in each polarity) and can be used to satisfy safety or other requirements. For example, if a sense resistor (resistor614) fails in an open state, the full loop supply voltage could appear at the ADC input pins and possibly propagate to other components, causing an unsafe situation. The diodes650here clamp or limit this voltage to one diode drop (approximately 0.6V). Note that it may be possible to place multiple diodes in series in place of each diode650, such as when two diodes are used in place of each diode650(in which case the voltage would be limited to two diode drops or approximately 1.2V).

A thermistor652is placed across a second pair of inputs AIN2of the analog-to-digital converter602. Two additional resistors654-656are coupled in series between the thermistor652and a PSW switch658. A voltage across the resistor654is provided to a third pair of inputs AIN3of the analog-to-digital converter602. A controller660controls the device600, such as by controlling the configurations of the inputs.

In particular embodiments, the transistors618-622,630-634,644may represent 400V/30 mA solid state relays (SSRs) in SO4 packages. The transistor646may represent a 400V/30 mA or 60V/0.5 A solid state relay in an SO4 package. The resistor614could represent a 10Ω or 2.05 kΩ resistor. The resistor616could represent a 100 kΩ resistor. The resistors628,638could represent 10Ω resistors. The resistors640-642could represent 0Ω resistors.

The components shown within the dashed lines ofFIG. 6may be selectively populated within a circuit, depending on the implementation. For example, in a first embodiment shown inFIG. 7, the resistors616and640may be omitted. In this embodiment, the first and second inputs604-606may be configured as HLAI current, LLAI, or digital inputs, and the third input608is configured as an HLAI current input. In this embodiment, the device600could have the following configurations of inputs.

In a second embodiment shown inFIG. 8, the diode612, the resistors638and642, and the transistor644may be omitted. In this embodiment, the first input604may be configured as an HLAI voltage, LLAI, or digital input. The second input606may be configured as an HLAI current, LLAI, or digital input. The third input608is configured as a digital output (DO). In this embodiment, the device600could have the following configurations of inputs and outputs.

InFIG. 6, the inputs604-606may represent “universal” inputs in that they can be reconfigured as (voltage or current) HLAI, LLAI, or digital inputs. Take input604as an example. In some embodiments, the resistor614is 10Ω, the diode612is present, and the resistor616is omitted as shown inFIG. 7. An HLAI current loop can be coupled to the input terminals610a-610bsuch that the current enters into terminal610b. The current flows through the resistor614and the diode612and out of terminal610a. If the current is a 0-20 mA loop current, this can generate a 0-200 mV drop across the resistor614. If the 10Ω resistor614has a 0.5% tolerance, the device600can be factory calibrated or otherwise calibrated in order to achieve a 0.1% or other measurement accuracy. For instance, a fixture that uses a two-point calibration (at ≧0 mA and ≦20 mA) could be used to calibrate the device600.

An LLAI source (such as a thermocouple or millivolt source like a 0-10 mV, 0-50 mV, or 0-100 mV source) can be coupled with its positive lead to the input terminal610aand its negative lead to the input terminal610b. As a particular example, a thermocouple could provide an input between −9.8 mV and 76 mV. With a 76 mV input, the diode612is reversed-biased. With a −9.8 mV input, the diode612is forward-biased but with an insignificant forward current. As another particular example, a millivolt source could provide a maximum input of 100 mV. In particular embodiments, there may be no need to factory calibrate or otherwise calibrate a thermocouple or millivolt source input.

A digital input source (such as a field-mounted switch) can be coupled across the input terminals610a-610b. The resistance of the switch can be measured by turning on the current source648, which in particular embodiments produces a 210 μA current. The current could flow out of the terminal610a, through the remote switch resistance (ideally 0Ω or open circuit), in through the terminal610b, out through the terminal636a, in through the terminal636b, through the thermistor652and the resistors654-656, and to the PSW switch658. The analog-to-digital converter602is configured to close the PSW switch658during this conversion, so the 210 μA current returns to ground via the PSW switch658.

If the remote switch is closed, this could be defined as having a maximum total resistance of 300Ω (100Ω for the remote switch and 200Ω for the wiring). In this case, a 210 μA current could generate a voltage drop between 0 mV and 63 mV, which can be measured by the analog-to-digital converter602at the AIN1input. This may be a “rough” calculation since the current source648could have an initial accuracy of ±5% with a 200 ppm/° C. temperature coefficient or other variable behavior. Since this is a digital measurement, an error (such as around 6.2%) in switch resistance measurements could be acceptable. Thus, the device600can define “switch closed” as a 0-67 mV measurement at the AIN1input.

When the remote switch is open, the 210 μA current bypasses the remote switch and instead flows through the clamping diodes650and then through the thermistor652, the resistors654-656, and the PSW switch658. Here, a current of about 105 μA flows through each of the two forward-biased clamping diodes650. Because of the current-voltage characteristics of the diodes650, the resulting voltage drop could be 365 mV or greater (where 365 mV may represent a worst case value). Thus, the device600can define “switch open” as any measurement at the AIN1input that is greater than 365 mV. Any measurement between 67 mV and 365 mV could be declared “indeterminate” and therefore “bad.”

In some embodiments, the resistor616is 100 kΩ (±0.1%), the diode612is omitted, and the resistor616is 2.05 kΩ as shown inFIG. 8. An HLAI voltage loop could be coupled to a voltage source, such as a low-impedance source between 0-5V or 1-5V. Since the input impedance of the input604is about 100 kΩ (100 kΩ+2.05 kΩ), the output impedance of the voltage source must be below 100Ω in order to meet a 0.1% or other specified accuracy. The positive terminal of the voltage source is coupled to the terminal610a, and the negative terminal of the voltage source is coupled to the terminal610b. An input signal is applied to a voltage divider formed by the resistors614-616. The resulting voltage (such as 0-0.1004V) can be measured at the AIN1input. Note that the voltage source could be coupled to the terminals610a-610bwith an opposite polarity than that described above. However, the analog-to-digital converter602would output values of the wrong polarity, and any component receiving the output values could be designed to handle the values' reversed polarity. In particular embodiments, the HLAI voltage input could be factory calibrated or otherwise calibrated, such as by using the same two-point calibration scheme described above.

AlthoughFIG. 6illustrates another example device600having at least one remotely configurable analog/digital input circuit, various changes may be made toFIG. 6. For example, the device600could include any number of reconfigurable inputs, such as a single input or more than two inputs. Also, any other or additional types of input sources could be coupled to a reconfigurable input. AlthoughFIGS. 7-8illustrate example configurations of the device600, various changes may be made toFIGS. 7-8. For instance, the device600could be configured in any other suitable manner.

FIGS. 9A-9Billustrate a more detailed example of a device900having at least one remotely configurable analog/digital input circuit according to this disclosure. As shown inFIG. 9, the device900may represent a more detailed example of the device600shown inFIG. 6. In this example, the transistors618-622,630-634,644-646are implemented using AQY214S high-voltage photo MOS relays. However, the transistors644-646could also be implemented using AQY212GS high-current photo MOS relays. The device900could be incorporated into any suitable device or system, such as a wireless leaf node or wired sensor fromFIG. 1.

AlthoughFIGS. 9A-9Billustrate a more detailed example of a device900having at least one remotely configurable analog/digital input circuit, various changes may be made toFIGS. 9A-9B. For example, the circuitry shown inFIGS. 9A-9Bcould be incorporated into any suitable device or system.

FIG. 10illustrates an example method1000for providing a remotely configurable analog/digital input according to this disclosure. As shown inFIG. 10, an input source is coupled to a reconfigurable input circuit at step1002. A configuration of the input circuit is remotely adjusted at step1004. This could include, for example, an operator using a wired or wireless device to provide configuration data to the input circuit, where the configuration data causes switches to open and/or close to configure the input circuit appropriately based on the input source being used. Input data can be provided from the input source to a circuit (such as an ADC) using the configured input circuit at step1006.

AlthoughFIG. 10illustrates an example method1000for providing a remotely configurable analog/digital input, various changes may be made toFIG. 10. For example, while shown as a series of steps, various steps inFIG. 10could overlap, occur in parallel, occur in a different order, or occur multiple times.