Products
MODEL 122-21PM1 TRANSMITTER EXCITATION/CONDITIONER MODULE
Description
The Model 122-12PM1 is 12 independent current sources and conditioning amplifiers, plus a power supply. All circuitry, with exception of the power transformer and one voltage regulator, is mounted on a single PC board which is mounted to a copy chassis in the unit.
Connection to the front and rear panels is made through Molex sockets and headers. Each signal
is grouped into one of two sets of six connections, which go to the front or rear panel from the PC board. Front panel connections go to all rotary switches and test jacks, while the rear panel connections go to terminal strips.
The power supply operates from standard 115 VAC (+10%) 60 Hz power and produces +15 volts
for the relays and +28 volts for the current sources.
Each channel consists of an independent current limited voltage source and a 250 ohm ±0.005% sense resistor. The current limit is set to approximately 30mA which will allow normal 4-20mA operation of the transmitter, but will protect the system +28 volt supply and the 250 ohm sense resistors from any accidental short-circuiting. This regulator also provides isolation from other channels so that if one channel is current limiting, the other 11 channels will continue to function.
The current output passes through the normally closed contacts. This relay can be opened by the front panel Current Monitor select rotary switch and momentary toggle switch. With the relay operated, the current path goes through the from panel Current Monitor jacks, where an external ammeter can be inserted to measure the actual loop current for calibration purposes. The design of the switching circuit allows only one channel to be monitored from the front panel at a time. The other channels
will not be affected by the operation of this monitor.
For a transmitter input range of 4-20mA of current, the resistor drops 1-5 volts. This 1-5 volt signal
is routed to the back panel “1-5 Volt Output” terminal strips and the front panel Output Monitor rotary switch.
Some 4-20mA transmitters are intelligent; that is, they have programmable ranges, calibrations,
self-tests, or other externally controlled functions. Of these intelligent transmitters, some communicate over the existing 4-20mA current loop lines using a high-frequency digital signal superimposed over the current signal. For these transmitters, a pair of test jacks on the front panel
is supplied to attach communications equipment directly across the transmitter terminals. One transmitter at a time may be selected for communication, using the Communicator Select rotary switch.
Specifications
Connections: Rear panel AC power receptacle and fuse 4-20mA current loop transmitter 1-5V DC output Front panel Power switch and indicator monitor jacks Output voltage monitor jacks Communicator select and monitor jacks Power: 115 VAC + 10%, 60Hz, 40 watts fully loaded |
