475 and signal generator
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The signal generator can provide a 4-20ma signal to the instrument; is 475 suitable?
It can be specified in some loop tests, but it’s not clear whether it works in the same way as when a signal is sent by 705
Sure, that’s the effect you get when performing a circuit check
There are two concepts here: a signal generator is capable of outputting a 4–20mA DC signal on its own, whereas 475 works by sending instructions to smart instruments that support the HART protocol, causing those instruments to output a 4–20mA signal.
475 allows the transmitter to supply a 4–20mA signal to the circuit during loop verification. When calibrating the instrument panel, only a signal generator can be used to send a 4–20mA signal.
The last edit to this post was made by budaoweng123 on 2015-12-14 at 16:53. It can be achieved indirectly, by using an intelligent transmitter that supports Hart to enter loot test mode via 475; this effectively turns it into a signal generator
In what situations is it necessary to use a signal generator instead of the 475?
When there are no smart instruments (that support Hart) or non-smart instruments, and it is necessary to measure the instrument circuit or calibrate the valve positioner, a signal generator is required. The signal generator can provide either active or passive signals as required; active signals are necessary for calibrating valves and for supplying signals to passive safety barriers.
Instruments that support HART communication can all be signaled using 475