Rugged instrumentation for reliable measurement and control

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E-Help Tip: Relay Alarm Output

Q. On a 4-20mA gas detector, while we replace the cell, the output reverts to 3mA. This causes the device receiving the 4-20mA signal to go into a critical alarm condition and can shut down a critical process. What device do you have that will keep the output at no less than 4mA?

It would also be convenient to have this instrument provide me with a 'relay alarm contact output' when my input goes to 3mA. It can be 24Vdc or 120Vac. It should be in a DIN housing.

 CPT hi low pp

A. Moore Industries CPT PC-Programmable Temperature Transmitter and Signal Isolator/Converter CPT/HLPRG/0-20MA/117AC*/-C [DIN] can be used for this application. A configuration cable is required to utilize the PC programming capability. The selected model will have the functions of the signal repeater with an alarm relay output. You can set the alarm fault relay to trigger at your choice of input signal level below 4mA.

The CPT has a menu selection for upper and lower limits. You can set 3.9mA low limit there.

Figure 2. PC Programmable

The SPA2 upper and lower limits must be defined by setting up a “custom curve” lookup table which (below), in this case, will be 5 points where in = out. By using the custom curve table, the output will not go below the lowest ordered pair or above the highest ordered pair. In this case it will define the lower output limit.

SPA2custom curve

Do you want more information? Download the data sheet. Or visit the catalog.

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