TC815 datasheet(14/26 Pages) MICROCHIP

14 / 26 page

TC815

DS21474B-page 14

6.0

-MEM OPERATING MODE

Bringing -MEM (Pin 61) momentarily low configures the

TC815 “-MEM” Operating mode. The -MEM LCD

Annunciator becomes active. In this Operating mode,

subsequent measurements are made relative to the last

two digits (-99) displayed at the time MEM is low. This

represents 5% of full scale. The last two significant digits

are stored and subtracted from all the following input

conversions. The following examples clarify operation:

EXAMPLE 6-1:

IN AUTO-RANGING

EXAMPLE 6-2:

IN FIXED RANGE

(200.0

Ω FULL SCALE)

EXAMPLE 6-3:

IN FIXED RANGE

On power-up, the TC815 “-MEM” mode is not active.

Once the “-MEM” is entered, bringing MEM low again,

it returns the TC815 to normal operation.

The “-MEM” mode is also cancelled whenever the mea-

surement type (resistance, voltage, current AC/DC,

Ω/LOΩ) or range is changed. The LCD -MEM annunci-

ator will be off in normal operation.

In the auto-range operation, if the following input signal

cannot be converted on the same range as the stored

value, the “-MEM” mode is cancelled. The LCD annun-

ciator is turned off.

The “-MEM” Operating mode can be very useful in

resistance measurements when lead length resistance

would cause measurement errors.

7.0

AUTOMATIC RANGE

SELECTION OPERATION

When power is first applied, the TC815 enters the auto-

range operating state. The Auto-Range mode may be

entered from Manual mode by changing the measure-

ment function (resistance or voltage), or by changing

the measurement option (AD/DC,

Ω/LOΩ).

The automatic voltage range selection begins on the

most sensitive scale first: 200mV for DC or 2.000V for

AC measurements. The voltage range selection flow

chart is given in Figure 7-1.

Internal input protection diodes to VDD (Pin 28) and

VSSA (Pin 57) clamp the input voltage. The external

10M

Ω input resistance (see Figure 7-1, R14 and R13)

limits current safely in an overrange condition.

The voltage range selection is designed to maximize

resolution. For input signals less than 9% of full scale

(count reading <180), the next most sensitive range is

selected.

An over range voltage input condition is flagged when-

ever the internal count exceeds 2000, by activating the

buzzer output (Pin 4). This 4kHz signal can directly

drive a piezo electric acoustic transducer. An out of

range input signal causes the 4kHz signal to be on

122msec, off for 122 msec, on for 122msec and off for

610msec (see Figure 11-1).

During voltage auto-range operation, the extended res-

olution feature operates on the 2000V range only. (See

Extended Resolution Operating mode discussion.)

The resistance automatic range selection procedure is

shown in Figure 7-2. The 200

Ω range is the first range

selected unless the TC815 low ohms resistance mea-

surement option is selected. In low ohms operation, the

first full scale range tried is 2k

Ω.

The resistance range selected maximizes sensitivity. If

the conversion results in a reading less than 180, the

next most sensitive full scale range is tried.

If the conversion is less than 19 in auto-range opera-

tion, a continuous 4kHz signal is output at BUZ (Pin 4).

An over range input does not activate the buzzer.

Out of range input conditions are displayed by a blink-

ing most significant digit with the three least significant

digits set to “000.”

The extended resolution feature operates only on the

2000k

Ω and 2000V full scale range during auto-range

operation. A blinking “1” most significant digit is inter-

preted as the digit 2. The three least significant digits

display data normally.

RI (N) = 18.21kΩ (20kΩ Range) = > Display 18.21kΩ

MEM

= > Store 0.21k

Ω

RI (N+1) = 19.87kΩ (20kΩ Range)

= > Display 19.87 - 0.21 = 19.66k

Ω

RI (N+2) = 22.65kΩ (200kΩ Range)

= > Display 22.7k

Ω and MEM disappears

RI (N) = 18.21kΩ = > Display 18.2kΩ

MEM

=> Store 8.2

Ω

RI (N+1) = 36.7Ω

= > Display 36.7 - 8.2 = 28.5

Ω

RI (N+2) = 5.8Ω

= > Display 5.8 = 2.4

Ω*

*Will display minus resistance if following input is

less than offset stored at fixed range.

VI (N) = 0.51V = > Display 0.51V

MEM

=>Store 0.51V

VI (N+1) = 3.68V

= > Display 3.68 - 0.51 = 3.17V

VI (N+2) = 0.23V

= > Display 0.23 - 0.51 = -0.28V

VI (N+3) = -5.21V

= > Display - 5.21 - 0.51 = -5.72V

TC815 数据表(PDF) 14 Page - Microchip Technology

TC815 数据表(HTML) 14 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

数据表下载