Shuichi Matsuda1 Yoshinori Sugawara1 Masayuki Fujiwara2
Yokogawa developed the YTMX580 multi-input temperature transmitter with eight- channel inputs and wireless communication functions conforming to the ISA100.11a standard. YTMX580 can accurately monitor temperatures at multi-points in hazardous areas to obtain the temperature distribution in the process industry, which reduces the number of transmitters and wires to be installed and curbs the total cost. This paper describes YTMX580's high performance in multipoint measurement, electric characteristics that enable long-term operation with batteries, and the enclosure which satisfies the requirements of being intrinsically safe, dust-proof, and waterproof.
Since 2010, Yokogawa has been providing wireless products conforming to the ISA100.11a wireless communication standard for industrial automation (IA)1 2. As a new addition to the lineup, Yokogawa has developed the YTMX580 multi-input temperature transmitter. Like the YTA510 temperature transmitter, YTMX580 is driven by batteries, but the number of its inputs has been increased from two to eight.
Like Yokogawa's existing wireless products, YTMX580 conforms to explosion proof standards, enabling operation in hazardous areas.
|Figure 1 External view of the YTMX580|
YTMX580 can accept signals from up to eight sensors such as IEC-conforming thermocouples (eight types including Types K, E, J) and resistance temperature detectors (three types including Pt100), then converts the corresponding measurement values to wireless signals and transmits them.
YTMX580 can also accept signals of DC voltage, resistance, and 4 - 20 mA DC current.
This model conforms to the ISA100.11a wireless communication standard and uses license-free 2.4 GHz band. In addition, it adopts the 128 bit Advanced Encryption Standard (AES) to ensure high security.
Figure 1 shows the external view of the YTMX580 and Table 1 shows its major specifications.
Table 1 Major specifications of YTMX580
|Wireless standard||ISA10 0.11a|
|Number of input points||8|
|Input signal*1||Thermocouples, RTD, DC voltage, resistance, 4 - 20 mA DC current (require an external shunt resistor)|
|Accuracy||Pt100: ± 0.3°C (lower than 400°C), Type K: ± 1.0°C, etc.|
|Cold junction compensation accuracy||± 0.5°C|
|Update period||1 sec to 3600 sec.|
|Battery life||6 years under the following conditions
Network connection: Jointed
Update period: 60 sec Role: I/O only
Ambient temperature: 23°C
LED indicator: Off
|Ambient temperature||- 40 to 85°C|
|Ambient humidity||0 to 100% RH|
|Protection class||IP66/IP67, NEMA Type 4X|
|Explosion proof specification||Intrinsic safety: FM, CSA, ATEX, IECEx certified; TIIS to be applied
Nonincendive protection: FM, CSA certified
|Mass||3.2 kg (without mounting brackets)|
*1: DC voltage and DC current are out of scope of the explosion proof certification
|Figure 2 Block diagram of the internal structure|
When considering the maintainability for users, it is desirable for wireless products to operate as long as possible without replacing batteries. With low-power consumption design and optimal power consumption control, the YTMX580 operates with an average current of 250 µA or less. As a result, it has a long battery life of up to six years at a measurement interval of 60 seconds. It can also perform eight-point measurement at an interval of two seconds as described before.
The following sections explain the technical measures to satisfy both high speed/multi channel measurement and battery life extension.
Reducing the Consumption Current
As shown in Figure 2, the internal structure of the main unit is composed of an input measurement unit, a display unit for indicating the status of the device, a wireless communication unit implementing the ISA100.11a communication function, an infrared communication unit for configuring the device by using the FieldMate4 or other tools, a power supply unit, a CPU, a ferroelectric random access memory (FeRAM), and so on. Each unit is designed to lower its power consumption by aggressively reducing the current consumed by it.
To reduce the consumption current further, the YTMX580 implements the intermittent operation controlled by the firmware shown in Figure 3. With intermittent operation, a sequence of processes is performed on the basis of the measurement cycle. Input measurement processing, communication processing, status checking, and so on are performed, and then the CPU is put in sleep mode to reduce unnecessary power consumption. To reduce the power consumption further, when the CPU is in sleep mode, the power supply to the input measurement unit is cut off, unnecessary built-in functions of the CPU are disabled, and the CPU clock is switched to the lower-speed sub clock. Likewise, low power consumption operation responding to the communication conditions is performed also in the wireless and infrared communication units.
|Figure 3 Intermittent Operation|
As the result of the power supply control, clock control and others described above, the YTMX580 achieves low consumption current of 50 µA or less in the sleep mode.
Although the method to cut off the power supply to the not operating circuits by power supply control is effective for reducing power consumption, this may complicate the interface with the other live circuits because of the necessity to clearly define the interface against the sudden cutoff of the power. However, the YTMX580 is designed applying simplified signal interfaces between the units so as not to affect the other circuits at the power cutoff.
Shortening the Operating Time
To reduce power consumption, it is indispensable to reduce the consumption current in each period of the intermittent operation cycle. As for the operating time in its cycle, the recovery time from the sleep mode needs to be taken into account.
|Figure 4 Battery pack|
If the measurement can be performed immediately after recovery from sleep mode, operating time can be shortened and the consumption current can be reduced. In fact, however, on-off control for the power supply circuit is performed, so measurement before the power becomes stable is affected in its input accuracy and stability. To shorten recovery time without affecting input accuracy and stability, the power supply circuit is rigorously verified and major circuit constants are adjusted, thus optimizing processing after the power up.
To achieve quick and stable measurement in as short a time period as possible at an interval of two seconds with eight inputs, the proven scanner method using solid state relays (SSR) is adopted as an input circuit. This scanner method, with the optimization of the input measurement sequence, can shorten the measurement time. Actually, it can perform three input measurement at an interval of one second.
Moreover, this scanner method can consolidate multiple AD converters to one, and lower power consumption in the input circuits.
Although the YTMX580 differs from other products in shape, structure and so on, considering the maintainability for users, it is designed to use the same accessories as those for Yokogawa's other wireless transmitters. Those accessories include the battery pack shown in Figure 4 and a remote antenna.
The YTMX580 also uses the same parameter structure as that of the existing YTA510 for user convenience, so that users can perform settings and operations for it via infrared communication using the FieldMate in the same way as for the other wireless transmitters.
For wireless communication, the YTMX580 conforms to the ISA100.11a standard to ensure its interoperability.
|Figure 5 Dust-proof test (above)
and waterproof test (below)
|Figure 6 Drain|
The glass window for infrared communication is placed at the hollow of the enclosure surface to protect it from extraneous shocks and so on, thus ensuring its safety.
This paper has described the features of the YTMX580 along with hardware, firmware, mechanical structures, and standardized designs for wireless products which implement those features. This model, with eight-channel multiple inputs, high-speed measurement performance, long battery life, explosion proof capability and other features, is best suited for temperature measurement in hazardous areas.
As a product constituting Yokogawa's wireless product lineup, the YTMX580 will continue evolving so as to respond to various customers' requests and market trends.
YTMX580 can accept inputs from up to 8 points of measurement such as thermocouples (8 types: K, E, J, etc.) or RTD signals (3 types: Pt100, etc.), converting the corresponding measurement input values to a wireless signal. It can also accept DC voltage, resistance, and 4 to 20 mA DC signal input.
Yokogawa offers a full line of temperature transmitters that are head-mounted, panel-mounted, or field-mounted.