Punch Tape Recording Rain Gage
Paper Tape
Description and Quality
Control
Purpose of this Page
The purpose of this page is two fold: (1) to describe the paper tape used on the Punch Tape Recording Rain Gage that is part of the Cooperative Observing Program of the National Weather Service (NWS); and (2) to describe how to perform quality control of these punch tapes.
Use these links to go directly to specific sections of this page.
Punch Tape Gage with access door open. The punch tape and punch mechanism inside the casing are visible through the open door.
Description of the Tape
The paper tape used on the NWS punch tape recording rain gage is classified as a strip chart. It is obtained from the NOAA Logistics Supply Center (NLSC) in rolls of 410 feet in length. It contains 450 sequentially numbered, 24 hour frames to accommodate a continuous record of precipitation that collects in the punch tape recording rain gage's bucket. Each individual frame is divided into 24 hours segments, identified from 1 to 24, with each hour divided into 15 minute increments to match the quarter hour punch cycle of this NWS electronic rain gage.
The amount of precipitation collected in the gage's bucket is transmitted to a punching mechanism which then records the amount to the nearest tenth of an inch as a series of holes punched in the tape (hence the name). An electronic timer cycles the gage every 15 minutes, corresponding to the 15 minute divisions on the tape. The series of punched holes run horizontally across the tape and are easily read and interpreted to the precipitation amount measured by the gage.
Interpreting the Tape
The interpretation of the tape must begin with an overview of its
layout. The tape is divided into 24 uniquely numbered hourly time
frames, each just under a foot in length. Sequential frame
numbers are printed in red
just after the beginning of each 24 hour frame. The time printed
on the tape is in military format (24-hour clock) where 9 PM is
indicated as 21 for the twenty-first hour of the day.
Note the two greyed lines, approximately 3/8 inch from each edge of the tape, that run the entire length of the tape. These lines are for reference punches which occur at each and every punch cycle regardless of the amount of precipitation in the gage's collection bucket. It is important to note that punches appearing in these greyed areas indicate to the optical tape reader that the gage is operational, even if no data holes are punched, i.e., for reading of 0.0 inches of precipitation.
Decoding the Punched Values: Each of the vertical divisions paralleling the greyed lines form a reference amount for the precipitation accumulated in the collection bucket. Look at the tape with the earliest hour in the 24 hour frame at the top. Each set of four vertical columns represent a digit in the accumulated precipitation amount. Gage measurements range from 0.0 through 19.9 inches, the maximum capacity of the gage.
Four sets of columns labeled 8-4-2-1 represent 4 unique digits in the accumulated precipitation measurement. The digit value is determined from the total punches within each set. In the table below, the "o" represents a punch in the columns which are labeled, from left to right, 8, 4, 2, and 1, respectively.
| 8 | 4 | 2 | 1 | Value |
| 0 | ||||
| o | 1 | |||
| o | 2 | |||
| o | o | 3 | ||
| o | 4 | |||
| o | o | 5 | ||
| o | o | 6 | ||
| o | o | o | 7 | |
| o | 8 | |||
| o | o | 9 |
This table above shows how each digit set would be punched for the numeric values 0 through 9. To obtain the numeric values, add up the column values that are punched. For those of you familiar with binary numbers, the punched columns represent the binary number for the numeric value where a hole equals 1 and no hole equals zero.
Returning to the tape, the first digit set on the right represents the tenths value of the gage's accumulated precipitation; the second set from the right represents whole inches; and the third set from the right represents 10s of inches. The fourth digit set (the left hand set) is not used by the gage because the maximum measurement is 19.9 inches.
As an example, one row on the tape might look like the following table:
| 8 | 4 | 2 | G | 1 | 8 | 4 | 2 | 1 | S | 8 | 4 | 2 | G | 1 | 8 | 4 | 2 | 1 | Value |
| o | o | O | o | o | o | o | o | 19.9 |
The value represented by this row of punches is 19.9 inches of accumulated precipitation. Ignoring the punches for the greyed lines (G) and the sprocket holes (S), the first digit set (on the left) is not punched, as expected. Working from left to right, the second digit set has one punch under "1"; the next digit set has two punches under "8" and "1"; and the third digit set has two punches under "8" and "1". These punches represent a value of 1,9,9 or, when decoded, 19.9 inches, the maximum gage measurement.
The code format for each row is known in the computer world as binary coded decimal or BCD.
As the precipitation amount increases with time, the accumulated amounts are punched out for each 15 minute time period thereby producing a complete record of precipitation versus time for the gage site. The increase in precipitation from one hour to the next can easily be determined by subtracting the two hourly totals to find the amount of precipitation that has fallen during the period.
Encoding the Punched Values: The gage mechanisms are designed to translate the precipitation measurement into holes on the punch tape. The gage mechanically reverses the process just described for decoding punch tape codes. Each digit of the gage's accumulated amount is transferred to the code disk and punch block as individual numbers (tenths, whole inches, and tens of inches). For example, punch holes record each digit of a value using the appropriate combination from the 8-4-2-1 digit set as needed to make the required digital value. An accumulated amount of precipitation in the gage's bucket which corresponds to 15.7 inches would appear punched on the tape as follows.
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