Thermistor temperature
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A temperature measurement port has been installed on the current equipment, but it is desired to connect it directly to the DCS. Go straight into SIS. How to achieve it in the best way. Two thermal resistors, or just one connected to SIS, and then communicated to the DCS? Or a better solution? Thank you
Two pairs are the best; if they are identical, a safety barrier at one inlet and two outlets will also work.
A dual-unit setup is better; use two units. If only a single unit has been ordered, use a one-input two-output safety barrier. It’s best to avoid using communication points, as they cause many failures and have slow response times
It is better to use two thermal resistors, as one signal is divided in the SIS into two parts that are sent separately to the SIS and the DCS; if this device fails, neither system will receive the signal, which poses a significant risk.
It is still recommended to use two units; otherwise, if problems arise in the future, neither system will be able to function. With two units, it’s also possible to compare the errors and such
If the temperature is only displayed in the DCS and not used for control, either single or dual channels are acceptable. If control is involved on the DCS, it is recommended to use a dual-pipe setup.
First of all, a single dual-channel setup exists only at the sensor level; you need a transmitter to integrate into the system. In any case, there is only one cable running from the transmitter to the cabinet, so it’s not possible to connect two transmitters within the sensor junction box. So you only need to consider whether to use communication or a one-in-two-out safety barrier; it is recommended to use a one-in-two-out safety barrier in the SIS. Of course, having two units is better, as it provides a backup option; if one set fails, only the wiring needs to be replaced, without having to replace the sensor.
With different systems, it’s better to use two.
It’s best to use two. The standard for SIS requires independent sampling. Therefore, it is not appropriate to send a signal to both DCS and SIS at the same time. Communication from SIS to DCS using a single link is allowed, but communication from DCS to SIS is not.
The dual thermistor is designed for measuring temperature with one in use and one as a backup, rather than for use in two separate systems. 1. First, check whether the SIS data from earlier was transmitted to the DCS. If the data was indeed sent to the DCS, then the signals coming from the field will be consistent with the original temperature signals entering the SIS; in this case, the system maintenance personnel can add a soft point in the DCS to receive the data from the SIS. 2. If there is no signal communication from the SIS to the DCS in the initial stage, and this temperature value needs to be sent to the DCS, then a two-way signal temperature transmitter can be used on the side of the SIS cabinet: one output is for the SIS and the other is for the DCS. It can also be sent directly to the SIS, thereby occupying one AO channel of the SIS, and then sent via hard wiring to the DCS AI channel. Using that approach, check whether there are sufficient spare points on site, or whether the SIS has enough space for temperature sensor installation, as well as consider factors such as procurement time. 3. In principle, it is necessary to ensure that the signals of the SIS system are normal first, in order to avoid introducing unnecessary signals or potential risks to the SIS.