GRS SyncroScan cTc code equipment:

G-R-S Syncroscan is a coded communication system for control and indication of remote functions.
These functions may be grouped at one location, or they may be situated at a large number of locations, widely spaced.
The system, therefore, may be used to handle one large interlocking, a group of interlockings,
or a section of centralized traffic control.

G-R-S Syncroscan is comprised of two seperate systems, one for controls, the other for indications,
operating independently of each other.
An all-relay system is used for the transmission of controls from the control office to the field locations.
A continuously scanning electronic system is used to bring in indications from the field stations.

CONTROLS The relay control system makes use of relays utilizing the free swings of mechanical oscillators - one at the control office and the other at the field locations - to create steps of a control cycle. These steps are equal units of time in the cycle, information being conveyed by the polarity of energy (or by frequency shift, if carrier is used for controls) on the line during each of the steps.

In the transmission of controls, a code cycle of 15 steps is used. The cycle time is 1-1/2 seconds. Thirteen of the steps handle the actual controls, each step being able to operate a two-position function, such as a switch or a single-direction signal. Generally, the first few steps are used to designate a "station", i.e., a particular group of controls, usually at a common location, such as those for a siding-end in cTc, or a portion of the switches or signals at an interlocking. For cTc, the 13 control steps may be assigned by varying combinations of stations plus controls. A typical arrangement might use 6 steps for station selection and 7 for controls. This would provide capacity for 64 stations with 7 controls per station.

Indication System Office Storage Unit

INDICATIONS The electronic indication system operates on independent carrier links between the control office and field stations. The scanning of indications is accomplished by sending pulses from the office via carrier link to the various field stations, checking the field functions to be indicated, and returning these pulses to the office on a different carrier link. It is possible to operate an entire Syncroscan system by carrier, using one frequency for controls and two for indications. In such an arrangement, no physical line is required.

Indication System Field Stepper Unit

The indication capacity of Syncroscan is large and very flexible. The positions of all field functions are scanned in sequence and indicated at the control office. As soon as a scanning cycle is completed, another follows immediately and automatically. Since the scanning rate is 100 indications per second, a system having 400 indications, for example, checks each indication every 4 seconds. When a field change occurs in an installation of this size, the indication change occurs at any time from immediately after to four seconds after the field change, depending upon the time of the change with respect to the scanning cycle. In no case would the interval exceed four seconds.

Indication System Office Carrier Unit

Both the office and field equipment are linked to the line via carrier receivers and transmitters, through filters. Frequency-shift carrier equipment is used. Each transmitter transmits on one or two closely spaced frequencies. Each receiver detects which of the two frequencies has been transmitted by its companion transmitter. The carrier link between the office and the field operates in a 1-kilocycle band centered at 6500 cycles-per-second. The carrier link from the field to the office operates in a 1-kilocycle band centered at 11000 cycles-per-second.

From: "G-R-S Sycnroscan, For cTc and remote control" - Pamphlet 876 - October, 1955.